ogl_tex.cpp

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/* Copyright (c) 2010 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * wrapper for all OpenGL texturing calls. provides caching, hotloading
 * and lifetime management.
 */

#include "precompiled.h"
#include "ogl_tex.h"

#include <cstdio>

#include "lib/app_hooks.h"
#include "lib/ogl.h"
#include "lib/bits.h"
#include "lib/sysdep/gfx.h"
#include "lib/tex/tex.h"

#include "lib/res/h_mgr.h"
#include "lib/fnv_hash.h"


//----------------------------------------------------------------------------
// OpenGL helper routines
//----------------------------------------------------------------------------

static bool filter_valid(GLint filter)
{
    switch(filter)
    {
    case GL_NEAREST:
    case GL_LINEAR:
    case GL_NEAREST_MIPMAP_NEAREST:
    case GL_LINEAR_MIPMAP_NEAREST:
    case GL_NEAREST_MIPMAP_LINEAR:
    case GL_LINEAR_MIPMAP_LINEAR:
        return true;
    default:
        return false;
    }
}


static bool wrap_valid(GLint wrap)
{
    switch(wrap)
    {
#if !CONFIG2_GLES
    case GL_CLAMP:
    case GL_CLAMP_TO_BORDER:
#endif
    case GL_CLAMP_TO_EDGE:
    case GL_REPEAT:
    case GL_MIRRORED_REPEAT:
        return true;
    default:
        return false;
    }
}


static bool are_mipmaps_needed(size_t width, size_t height, GLint filter)
{
    // can't upload the entire texture; we're going to skip some
    // levels until it no longer exceeds the OpenGL dimension limit.
    if((GLint)width > ogl_max_tex_size || (GLint)height > ogl_max_tex_size)
        return true;

    switch(filter)
    {
    case GL_NEAREST_MIPMAP_NEAREST:
    case GL_LINEAR_MIPMAP_NEAREST:
    case GL_NEAREST_MIPMAP_LINEAR:
    case GL_LINEAR_MIPMAP_LINEAR:
        return true;
    default:
        return false;
    }
}


static bool fmt_is_s3tc(GLenum fmt)
{
    switch(fmt)
    {
    case GL_COMPRESSED_RGB_S3TC_DXT1_EXT:
    case GL_COMPRESSED_RGBA_S3TC_DXT1_EXT:
#if !CONFIG2_GLES
    case GL_COMPRESSED_RGBA_S3TC_DXT3_EXT:
    case GL_COMPRESSED_RGBA_S3TC_DXT5_EXT:
#endif
        return true;
    default:
        return false;
    }
}


// determine OpenGL texture format, given <bpp> and Tex <flags>.
static GLint choose_fmt(size_t bpp, size_t flags)
{
    const bool alpha = (flags & TEX_ALPHA) != 0;
    const bool bgr   = (flags & TEX_BGR  ) != 0;
    const bool grey  = (flags & TEX_GREY ) != 0;
    const size_t dxt   = flags & TEX_DXT;

    // S3TC
    if(dxt != 0)
    {
        switch(dxt)
        {
        case DXT1A:
            return GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
        case 1:
            return GL_COMPRESSED_RGB_S3TC_DXT1_EXT;
#if !CONFIG2_GLES
        case 3:
            return GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
        case 5:
            return GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
#endif
        default:
            DEBUG_WARN_ERR(ERR::LOGIC); // invalid DXT value
            return 0;
        }
    }

    // uncompressed
    switch(bpp)
    {
    case 8:
        ENSURE(grey);
        return GL_LUMINANCE;
    case 16:
        return GL_LUMINANCE_ALPHA;
    case 24:
        ENSURE(!alpha);
#if CONFIG2_GLES
        // GLES never supports BGR
        ENSURE(!bgr);
        return GL_RGB;
#else
        return bgr? GL_BGR : GL_RGB;
#endif
    case 32:
        ENSURE(alpha);
        // GLES can support BGRA via GL_EXT_texture_format_BGRA8888
        // (TODO: can we rely on support for that extension?)
        return bgr? GL_BGRA_EXT : GL_RGBA;
    default:
        DEBUG_WARN_ERR(ERR::LOGIC); // invalid bpp
        return 0;
    }

    UNREACHABLE;
}


//----------------------------------------------------------------------------
// quality mechanism
//----------------------------------------------------------------------------

static GLint default_filter = GL_LINEAR;    // one of the GL *minify* filters
static int default_q_flags = OGL_TEX_FULL_QUALITY;  // OglTexQualityFlags

static bool q_flags_valid(int q_flags)
{
    const size_t bits = OGL_TEX_FULL_QUALITY|OGL_TEX_HALF_BPP|OGL_TEX_HALF_RES;
    // unrecognized bits are set - invalid
    if((q_flags & ~bits) != 0)
        return false;
    // "full quality" but other reduction bits are set - invalid
    if(q_flags & OGL_TEX_FULL_QUALITY && q_flags & ~OGL_TEX_FULL_QUALITY)
        return false;
    return true;
}


// change default settings - these affect performance vs. quality.
// may be overridden for individual textures via parameter to
// ogl_tex_upload or ogl_tex_set_filter, respectively.
// 
// pass 0 to keep the current setting; defaults and legal values are:
// - q_flags: OGL_TEX_FULL_QUALITY; combination of OglTexQualityFlags 
// - filter: GL_LINEAR; any valid OpenGL minification filter
void ogl_tex_set_defaults(int q_flags, GLint filter)
{
    if(q_flags)
    {
        ENSURE(q_flags_valid(q_flags));
        default_q_flags = q_flags;
    }

    if(filter)
    {
        ENSURE(filter_valid(filter));
        default_filter = filter;
    }
}


// choose an internal format for <fmt> based on the given q_flags.
static GLint choose_int_fmt(GLenum fmt, int q_flags)
{
    // true => 4 bits per component; otherwise, 8
    const bool half_bpp = (q_flags & OGL_TEX_HALF_BPP) != 0;

    // early-out for S3TC textures: they don't need an internal format
    // (because upload is via glCompressedTexImage2DARB), but we must avoid
    // triggering the default case below. we might as well return a
    // meaningful value (i.e. int_fmt = fmt).
    if(fmt_is_s3tc(fmt))
        return fmt;

#if CONFIG2_GLES

    UNUSED2(half_bpp);

    // GLES only supports internal format == external format
    return fmt;

#else

    switch(fmt)
    {
    // 8bpp
    case GL_LUMINANCE:
        return half_bpp? GL_LUMINANCE4 : GL_LUMINANCE8;
    case GL_INTENSITY:
        return half_bpp? GL_INTENSITY4 : GL_INTENSITY8;
    case GL_ALPHA:
        return half_bpp? GL_ALPHA4 : GL_ALPHA8;

    // 16bpp
    case GL_LUMINANCE_ALPHA:
        return half_bpp? GL_LUMINANCE4_ALPHA4 : GL_LUMINANCE8_ALPHA8;

    // 24bpp
    case GL_RGB:
    case GL_BGR:    // note: BGR can't be used as internal format
        return half_bpp? GL_RGB4 : GL_RGB8;

    // 32bpp
    case GL_RGBA:
    case GL_BGRA:   // note: BGRA can't be used as internal format
        return half_bpp? GL_RGBA4 : GL_RGBA8;

    default:
        {
        wchar_t buf[100];
        swprintf_s(buf, ARRAY_SIZE(buf), L"choose_int_fmt: fmt 0x%x isn't covered! please add it", fmt);
        DEBUG_DISPLAY_ERROR(buf);
        DEBUG_WARN_ERR(ERR::LOGIC); // given fmt isn't covered! please add it.
        // fall back to a reasonable default
        return half_bpp? GL_RGB4 : GL_RGB8;
        }
    }

    UNREACHABLE;

#endif  // #if CONFIG2_GLES
}


//----------------------------------------------------------------------------
// texture state to allow seamless reload
//----------------------------------------------------------------------------

// see "Texture Parameters" in docs.

// all GL state tied to the texture that must be reapplied after reload.
// (this mustn't get too big, as it's stored in the already sizeable OglTex)
struct OglTexState
{
    // glTexParameter
    // note: there are more options, but they do not look to
    //       be important and will not be applied after a reload!
    //       in particular, LOD_BIAS isn't needed because that is set for
    //       the entire texturing unit via glTexEnv.
    // .. texture filter
    //    note: this is the minification filter value; magnification filter
    //          is GL_NEAREST if it's GL_NEAREST, otherwise GL_LINEAR.
    //          we don't store mag_filter explicitly because it
    //          doesn't appear useful - either apps can tolerate LINEAR, or
    //          mipmaps aren't called for and filter could be NEAREST anyway).
    GLint filter;
    // .. wrap mode
    GLint wrap_s;
    GLint wrap_t;
    // .. anisotropy
    //    note: ignored unless EXT_texture_filter_anisotropic is supported.
    GLfloat anisotropy;
};


// fill the given state object with default values.
static void state_set_to_defaults(OglTexState* ots)
{
    ots->filter = default_filter;
    ots->wrap_s = GL_REPEAT;
    ots->wrap_t = GL_REPEAT;
    ots->anisotropy = 1.0f;
}


// send all state to OpenGL (actually the currently bound texture).
// called from ogl_tex_upload.
static void state_latch(OglTexState* ots)
{
    // filter
    const GLint filter = ots->filter;
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, filter);
    const GLint mag_filter = (filter == GL_NEAREST)? GL_NEAREST : GL_LINEAR;
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, mag_filter);

    // wrap
    const GLint wrap_s = ots->wrap_s;
    const GLint wrap_t = ots->wrap_t;
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, wrap_s);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, wrap_t);
    // .. only CLAMP and REPEAT are guaranteed to be available.
    //    if we're using one of the others, we squelch the error that
    //    may have resulted if this GL implementation is old.
#if !CONFIG2_GLES
    if((wrap_s != GL_CLAMP && wrap_s != GL_REPEAT) || (wrap_t != GL_CLAMP && wrap_t != GL_REPEAT))
        ogl_SquelchError(GL_INVALID_ENUM);
#endif

    // anisotropy
    const GLfloat anisotropy = ots->anisotropy;
    if (anisotropy != 1.0f && ogl_tex_has_anisotropy())
    {
        glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, anisotropy);
    }
}


//----------------------------------------------------------------------------
// texture resource object
//----------------------------------------------------------------------------

// ideally we would split OglTex into data and state objects as in
// SndData / VSrc. this gives us the benefits of caching while still
// leaving each "instance" (state object, which owns a data reference)
// free to change its state. however, unlike in OpenAL, there is no state
// independent of the data object - all parameters are directly tied to the
// GL texture object. therefore, splitting them up is impossible.
// (we shouldn't even keep the texel data in memory since that's already
// covered by the FS cache).
//
// given that multiple "instances" share the state stored here, we conclude:
// - a refcount is necessary to prevent ogl_tex_upload from freeing
//   <t> as long as other instances are active.
// - concurrent use risks cross-talk (if the 2nd "instance" changes state and
//   the first is reloaded, its state may change to that of the 2nd)
//
// as bad as it sounds, the latter issue isn't a problem: we do not expect
// multiple instances of the same texture where someone changes its filter.
// even if it is reloaded, the differing state is not critical.
// the alternative is even worse: disabling *all* caching/reuse would
// really hurt performance and h_mgr doesn't support only disallowing
// reuse of active objects (this would break the index lookup code, since
// multiple instances may then exist).

// note: make sure these values fit inside OglTex.flags (only 16 bits)
enum OglTexFlags
{
    // "the texture is currently uploaded"; reset in dtor.
    OT_IS_UPLOADED = 1,

    // "the enclosed Tex object is valid and holds a texture";
    // reset in dtor and after ogl_tex_upload's tex_free.
    OT_TEX_VALID = 2,
    //size_t tex_valid : 1;

    // "reload() should automatically re-upload the texture" (because
    // it had been uploaded before the reload); never reset.
    OT_NEED_AUTO_UPLOAD = 4,

    // (used for validating flags)
    OT_ALL_FLAGS = OT_IS_UPLOADED|OT_TEX_VALID|OT_NEED_AUTO_UPLOAD
};

struct OglTex
{
    Tex t;

    // allocated by OglTex_reload; indicates the texture is currently uploaded.
    GLuint id;

    // ogl_tex_upload calls choose_fmt to determine these from <t>.
    // however, its caller may override those values via parameters.
    // note: these are stored here to allow retrieving via ogl_tex_get_format;
    // they are only used within ogl_tex_upload.
    GLenum fmt;
    GLint int_fmt;

    OglTexState state;

    // OglTexQualityFlags
    u8 q_flags;

    // to which Texture Mapping Unit was this bound?
    u8 tmu;

    u16 flags;
};

H_TYPE_DEFINE(OglTex);

static void OglTex_init(OglTex* ot, va_list args)
{
    Tex* wrapped_tex = va_arg(args, Tex*);
    if(wrapped_tex)
    {
        ot->t = *wrapped_tex;
        // indicate ot->t is now valid, thus skipping loading from file.
        // note: ogl_tex_wrap prevents actual reloads from happening.
        ot->flags |= OT_TEX_VALID;
    }

    state_set_to_defaults(&ot->state);
    ot->q_flags = default_q_flags;
}

static void OglTex_dtor(OglTex* ot)
{
    if(ot->flags & OT_TEX_VALID)
    {
        tex_free(&ot->t);
        ot->flags &= ~OT_TEX_VALID;
    }

    // note: do not check if OT_IS_UPLOADED is set, because we allocate
    // OglTex.id without necessarily having done an upload.
    glDeleteTextures(1, &ot->id);
    ot->id = 0;
    ot->flags &= ~OT_IS_UPLOADED;
}

static Status OglTex_reload(OglTex* ot, const PIVFS& vfs, const VfsPath& pathname, Handle h)
{
    // we're reusing a freed but still in-memory OglTex object
    if(ot->flags & OT_IS_UPLOADED)
        return INFO::OK;

    // if we don't already have the texture in memory (*), load from file.
    // * this happens if the texture is "wrapped".
    if(!(ot->flags & OT_TEX_VALID))
    {
        shared_ptr<u8> file; size_t fileSize;
        RETURN_STATUS_IF_ERR(vfs->LoadFile(pathname, file, fileSize));
        if(tex_decode(file, fileSize, &ot->t) >= 0)
            ot->flags |= OT_TEX_VALID;
    }

    glGenTextures(1, &ot->id);

    // if it had already been uploaded before this reload,
    // re-upload it (this also does state_latch).
    if(ot->flags & OT_NEED_AUTO_UPLOAD)
        (void)ogl_tex_upload(h);

    return INFO::OK;
}

static Status OglTex_validate(const OglTex* ot)
{
    if(ot->flags & OT_TEX_VALID)
    {
        RETURN_STATUS_IF_ERR(tex_validate(&ot->t));

        // width, height
        // (note: this is done here because tex.cpp doesn't impose any
        // restrictions on dimensions, while OpenGL does).
        size_t w = ot->t.w;
        size_t h = ot->t.h;
        // .. == 0; texture file probably not loaded successfully.
        if(w == 0 || h == 0)
            WARN_RETURN(ERR::_11);
        // .. not power-of-2.
        //    note: we can't work around this because both NV_texture_rectangle
        //    and subtexture require work for the client (changing tex coords).
        //    TODO: ARB_texture_non_power_of_two
        if(!is_pow2(w) || !is_pow2(h))
            WARN_RETURN(ERR::_13);

        // no longer verify dimensions are less than ogl_max_tex_size,
        // because we just use the higher mip levels in that case.
    }

    // texture state
    if(!filter_valid(ot->state.filter))
        WARN_RETURN(ERR::_14);
    if(!wrap_valid(ot->state.wrap_s))
        WARN_RETURN(ERR::_15);
    if(!wrap_valid(ot->state.wrap_t))
        WARN_RETURN(ERR::_16);

    // misc
    if(!q_flags_valid(ot->q_flags))
        WARN_RETURN(ERR::_17);
    if(ot->tmu >= 128)  // unexpected that there will ever be this many
        WARN_RETURN(ERR::_18);
    if(ot->flags > OT_ALL_FLAGS)
        WARN_RETURN(ERR::_19);
    // .. note: don't check ot->fmt and ot->int_fmt - they aren't set
    //    until during ogl_tex_upload.

    return INFO::OK;
}

static Status OglTex_to_string(const OglTex* ot, wchar_t* buf)
{
    swprintf_s(buf, H_STRING_LEN, L"OglTex id=%u flags=%x", ot->id, (unsigned int)ot->flags);
    return INFO::OK;
}


// load and return a handle to the texture given in <pathname>.
// for a list of supported formats, see tex.h's tex_load.
Handle ogl_tex_load(const PIVFS& vfs, const VfsPath& pathname, size_t flags)
{
    Tex* wrapped_tex = 0;   // we're loading from file
    return h_alloc(H_OglTex, vfs, pathname, flags, wrapped_tex);
}


// return Handle to an existing object, if it has been loaded and
// is still in memory; otherwise, a negative error code.
Handle ogl_tex_find(const VfsPath& pathname)
{
    const uintptr_t key = fnv_hash(pathname.string().c_str(), pathname.string().length()*sizeof(pathname.string()[0]));
    return h_find(H_OglTex, key);
}


// make the given Tex object ready for use as an OpenGL texture
// and return a handle to it. this will be as if its contents
// had been loaded by ogl_tex_load.
//
// we need only add bookkeeping information and "wrap" it in
// a resource object (accessed via Handle), hence the name.
//
// <fn> isn't strictly needed but should describe the texture so that
// h_filename will return a meaningful comment for debug purposes.
// note: because we cannot guarantee that callers will pass distinct
// "filenames", caching is disabled for the created object. this avoids
// mistakenly reusing previous objects that share the same comment.
Handle ogl_tex_wrap(Tex* t, const PIVFS& vfs, const VfsPath& pathname, size_t flags)
{
    // this object may not be backed by a file ("may", because
    // someone could do tex_load and then ogl_tex_wrap).
    // if h_mgr asks for a reload, the dtor will be called but
    // we won't be able to reconstruct it. therefore, disallow reloads.
    // (they are improbable anyway since caller is supposed to pass a
    // 'descriptive comment' instead of filename, but don't rely on that)
    // also disable caching as explained above.
    flags |= RES_DISALLOW_RELOAD|RES_NO_CACHE;
    return h_alloc(H_OglTex, vfs, pathname, flags, t);
}


// free all resources associated with the texture and make further
// use of it impossible. (subject to refcount)
Status ogl_tex_free(Handle& ht)
{
    return h_free(ht, H_OglTex);
}


//----------------------------------------------------------------------------
// state setters (see "Texture Parameters" in docs)
//----------------------------------------------------------------------------

// we require the below functions be called before uploading; this avoids
// potentially redundant glTexParameter calls (we'd otherwise need to always
// set defaults because we don't know if an override is forthcoming).

// raise a debug warning if the texture has already been uploaded
// (except in the few cases where this is allowed; see below).
// this is so that you will notice incorrect usage - only one instance of a
// texture should be active at a time, because otherwise they vie for
// control of one shared OglTexState.
static void warn_if_uploaded(Handle ht, const OglTex* ot)
{
#ifndef NDEBUG
    // we do not require users of this module to remember if they've
    // already uploaded a texture (inconvenient). since they also can't
    // tell if the texture was newly loaded (due to h_alloc interface),
    // we have to squelch this warning in 2 cases:
    // - it's ogl_tex_loaded several times (i.e. refcount > 1) and the
    //   caller (typically a higher-level LoadTexture) is setting filter etc.
    // - caller is using our Handle as a caching mechanism, and calls
    //   ogl_tex_set_* before every use of the texture. note: this
    //   need not fall under the above check, e.g. if freed but cached.
    //   workaround is that ogl_tex_set_* won't call us if the
    //   same state values are being set (harmless anyway).
    intptr_t refs = h_get_refcnt(ht);
    if(refs > 1)
        return; // don't complain

    if(ot->flags & OT_IS_UPLOADED)
        DEBUG_WARN_ERR(ERR::LOGIC); // ogl_tex_set_*: texture already uploaded and shouldn't be changed
#else
    // (prevent warnings; the alternative of wrapping all call sites in
    // #ifndef is worse)
    UNUSED2(ht);
    UNUSED2(ot);
#endif
}


// override default filter (as set above) for this texture.
// must be called before uploading (raises a warning if called afterwards).
// filter is as defined by OpenGL; it is applied for both minification and
// magnification (for rationale and details, see OglTexState)
Status ogl_tex_set_filter(Handle ht, GLint filter)
{
    H_DEREF(ht, OglTex, ot);

    if(!filter_valid(filter))
        WARN_RETURN(ERR::INVALID_PARAM);

    if(ot->state.filter != filter)
    {
        warn_if_uploaded(ht, ot);
        ot->state.filter = filter;
    }
    return INFO::OK;
}


// override default wrap mode (GL_REPEAT) for this texture.
// must be called before uploading (raises a warning if called afterwards).
// wrap is as defined by OpenGL.
Status ogl_tex_set_wrap(Handle ht, GLint wrap_s, GLint wrap_t)
{
    H_DEREF(ht, OglTex, ot);

    if(!wrap_valid(wrap_s))
        WARN_RETURN(ERR::INVALID_PARAM);

    if(!wrap_valid(wrap_t))
        WARN_RETURN(ERR::INVALID_PARAM);

    if(ot->state.wrap_s != wrap_s || ot->state.wrap_t != wrap_t)
    {
        warn_if_uploaded(ht, ot);
        ot->state.wrap_s = wrap_s;
        ot->state.wrap_t = wrap_t;
    }
    return INFO::OK;
}


// override default anisotropy for this texture.
// must be called before uploading (raises a warning if called afterwards).
Status ogl_tex_set_anisotropy(Handle ht, GLfloat anisotropy)
{
    H_DEREF(ht, OglTex, ot);

    if(anisotropy < 1.0f)
        WARN_RETURN(ERR::INVALID_PARAM);

    if(ot->state.anisotropy != anisotropy)
    {
        warn_if_uploaded(ht, ot);
        ot->state.anisotropy = anisotropy;
    }
    return INFO::OK;
}


//----------------------------------------------------------------------------
// upload
//----------------------------------------------------------------------------

// OpenGL has several features that are helpful for uploading but not
// available in all implementations. we check for their presence but
// provide for user override (in case they don't work on a card/driver
// combo we didn't test).

// tristate; -1 is undecided
static int have_auto_mipmap_gen = -1;
static int have_s3tc = -1;
static int have_anistropy = -1;

// override the default decision and force/disallow use of the
// given feature. should be called from ah_override_gl_upload_caps.
void ogl_tex_override(OglTexOverrides what, OglTexAllow allow)
{
    ENSURE(allow == OGL_TEX_ENABLE || allow == OGL_TEX_DISABLE);
    const bool enable = (allow == OGL_TEX_ENABLE);

    switch(what)
    {
    case OGL_TEX_S3TC:
        have_s3tc = enable;
        break;
    case OGL_TEX_AUTO_MIPMAP_GEN:
        have_auto_mipmap_gen = enable;
        break;
    case OGL_TEX_ANISOTROPY:
        have_anistropy = enable;
        break;
    default:
        DEBUG_WARN_ERR(ERR::LOGIC); // invalid <what>
        break;
    }
}


// detect caps (via OpenGL extension list) and give an app_hook the chance to
// override this (e.g. via list of card/driver combos on which S3TC breaks).
// called once from the first ogl_tex_upload.
static void detect_gl_upload_caps()
{
    // note: gfx_card will be empty if running in quickstart mode;
    // in that case, we won't be able to check for known faulty cards.

    // detect features, but only change the variables if they were at
    // "undecided" (if overrides were set before this, they must remain).
    if(have_auto_mipmap_gen == -1)
    {
        have_auto_mipmap_gen = ogl_HaveExtension("GL_SGIS_generate_mipmap");
    }
    if(have_s3tc == -1)
    {
#if CONFIG2_GLES
        // some GLES implementations have GL_EXT_texture_compression_dxt1
        // but that only supports DXT1 so we can't use it anyway
        have_s3tc = 0;
#else
        // note: we don't bother checking for GL_S3_s3tc - it is incompatible
        // and irrelevant (was never widespread).
        have_s3tc = ogl_HaveExtensions(0, "GL_ARB_texture_compression", "GL_EXT_texture_compression_s3tc", NULL) == 0;
#endif
    }
    if(have_anistropy == -1)
    {
        have_anistropy = ogl_HaveExtension("GL_EXT_texture_filter_anisotropic");
    }

    // allow app hook to make ogl_tex_override calls
    if(AH_IS_DEFINED(override_gl_upload_caps))
    {
        ah_override_gl_upload_caps();
    }
    // no app hook defined - have our own crack at blacklisting some hardware.
    else
    {
        const std::wstring cardName = gfx::CardName();
        // rationale: janwas's laptop's S3 card blows up if S3TC is used
        // (oh, the irony). it'd be annoying to have to share this between all
        // projects, hence this default implementation here.
        if(cardName == L"S3 SuperSavage/IXC 1014")
            ogl_tex_override(OGL_TEX_S3TC, OGL_TEX_DISABLE);
    }
}


// take care of mipmaps. if they are called for by <filter>, either
// arrange for OpenGL to create them, or see to it that the Tex object
// contains them (if need be, creating them in software).
// sets *plevels_to_skip to influence upload behavior (depending on
// whether mipmaps are needed and the quality settings).
// returns 0 to indicate success; otherwise, caller must disable
// mipmapping by switching filter to e.g. GL_LINEAR.
static Status get_mipmaps(Tex* t, GLint filter, int q_flags, int* plevels_to_skip)
{
    // decisions:
    // .. does filter call for uploading mipmaps?
    const bool need_mipmaps = are_mipmaps_needed(t->w, t->h, filter);
    // .. does the image data include mipmaps? (stored as separate
    //    images after the regular texels)
    const bool includes_mipmaps = (t->flags & TEX_MIPMAPS) != 0;
    // .. is this texture in S3TC format? (more generally, "compressed")
    const bool is_s3tc = (t->flags & TEX_DXT) != 0;

    *plevels_to_skip = TEX_BASE_LEVEL_ONLY;
    if(!need_mipmaps)
        return INFO::OK;

    // image already contains pregenerated mipmaps; we need do nothing.
    // this is the nicest case, because they are fastest to load
    // (no extra processing needed) and typically filtered better than
    // if automatically generated.
    if(includes_mipmaps)
        *plevels_to_skip = 0;   // t contains mipmaps
    // OpenGL supports automatic generation; we need only
    // activate that and upload the base image.
#if !CONFIG2_GLES
    else if(have_auto_mipmap_gen)
    {
        // note: we assume GL_GENERATE_MIPMAP and GL_GENERATE_MIPMAP_SGIS
        // have the same values - it's heavily implied by the spec
        // governing 'promoted' ARB extensions and just plain makes sense.
        glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
    }
#endif
    // image is S3TC-compressed and the previous 2 alternatives weren't
    // available; we're going to cheat and just disable mipmapping.
    // rationale: having tex_transform add mipmaps would be slow (since
    // all<->all transforms aren't implemented, it'd have to decompress
    // from S3TC first), and DDS images ought to include mipmaps!
    else if(is_s3tc)
        return ERR::FAIL;   // NOWARN
    // image is uncompressed and we're on an old OpenGL implementation;
    // we will generate mipmaps in software.
    else
    {
        RETURN_STATUS_IF_ERR(tex_transform_to(t, t->flags|TEX_MIPMAPS));
        *plevels_to_skip = 0;   // t contains mipmaps
    }

    // t contains mipmaps; we can apply our resolution reduction trick:
    if(*plevels_to_skip == 0)
    {
        // if OpenGL's texture dimension limit is too small, use the
        // higher mipmap levels. NB: the minimum guaranteed size is
        // far too low, and menu background textures may be large.
        GLint w = (GLint)t->w, h = (GLint)t->h;
        while(w > ogl_max_tex_size || h > ogl_max_tex_size)
        {
            (*plevels_to_skip)++;
            w /= 2; h /= 2; // doesn't matter if either dimension drops to 0
        }

        // this saves texture memory by skipping some of the lower
        // (high-resolution) mip levels.
        //
        // note: we don't just use GL_TEXTURE_BASE_LEVEL because it would
        // require uploading unused levels, which is wasteful.
        // .. can be expanded to reduce to 1/4, 1/8 by encoding factor in q_flags.
        if(q_flags & OGL_TEX_HALF_RES)
            (*plevels_to_skip)++;
    }

    return INFO::OK;
}


// tex_util_foreach_mipmap callbacks: upload the given level to OpenGL.

struct UploadParams
{
    GLenum fmt;
    GLint int_fmt;
};

static void upload_level(size_t level, size_t level_w, size_t level_h, const u8* RESTRICT level_data, size_t UNUSED(level_data_size), void* RESTRICT cbData)
{
    const UploadParams* up = (const UploadParams*)cbData;
    glTexImage2D(GL_TEXTURE_2D, (GLint)level, up->int_fmt, (GLsizei)level_w, (GLsizei)level_h, 0, up->fmt, GL_UNSIGNED_BYTE, level_data);
}

static void upload_compressed_level(size_t level, size_t level_w, size_t level_h, const u8* RESTRICT level_data, size_t level_data_size, void* RESTRICT cbData)
{
    const UploadParams* up = (const UploadParams*)cbData;
    pglCompressedTexImage2DARB(GL_TEXTURE_2D, (GLint)level, up->fmt, (GLsizei)level_w, (GLsizei)level_h, 0, (GLsizei)level_data_size, level_data);
}

// upload the texture in the specified (internal) format.
// split out of ogl_tex_upload because it was too big.
//
// pre: <t> is valid for OpenGL use; texture is bound.
static void upload_impl(Tex* t, GLenum fmt, GLint int_fmt, int levels_to_skip)
{
    const GLsizei w  = (GLsizei)t->w;
    const GLsizei h  = (GLsizei)t->h;
    const size_t bpp   = t->bpp;
    const u8* data = (const u8*)tex_get_data(t);
    const UploadParams up = { fmt, int_fmt };

    if(t->flags & TEX_DXT)
        tex_util_foreach_mipmap(w, h, bpp, data, levels_to_skip, 4, upload_compressed_level, (void*)&up);
    else
        tex_util_foreach_mipmap(w, h, bpp, data, levels_to_skip, 1, upload_level, (void*)&up);
}


// upload the texture to OpenGL.
// if not 0, parameters override the following:
//   fmt_ovr     : OpenGL format (e.g. GL_RGB) decided from bpp / Tex flags;
//   q_flags_ovr : global default "quality vs. performance" flags;
//   int_fmt_ovr : internal format (e.g. GL_RGB8) decided from fmt / q_flags.
//
// side effects:
// - enables texturing on TMU 0 and binds the texture to it;
// - frees the texel data! see ogl_tex_get_data.
Status ogl_tex_upload(const Handle ht, GLenum fmt_ovr, int q_flags_ovr, GLint int_fmt_ovr)
{
    ONCE(detect_gl_upload_caps());

    H_DEREF(ht, OglTex, ot);
    Tex* t = &ot->t;
    ENSURE(q_flags_valid(q_flags_ovr));
    // we don't bother verifying *fmt_ovr - there are too many values

    // upload already happened; no work to do.
    // (this also happens if a cached texture is "loaded")
    if(ot->flags & OT_IS_UPLOADED)
        return INFO::OK;

    if(ot->flags & OT_TEX_VALID)
    {
        // decompress S3TC if that's not supported by OpenGL.
        if((t->flags & TEX_DXT) && !have_s3tc)
            (void)tex_transform_to(t, t->flags & ~TEX_DXT);

        // determine fmt and int_fmt, allowing for user override.
        ot->fmt = choose_fmt(t->bpp, t->flags);
        if(fmt_ovr) ot->fmt = fmt_ovr;
        if(q_flags_ovr) ot->q_flags = q_flags_ovr;
        ot->int_fmt = choose_int_fmt(ot->fmt, ot->q_flags);
        if(int_fmt_ovr) ot->int_fmt = int_fmt_ovr;

        // now actually send to OpenGL:
        ogl_WarnIfError();
        {
            // (note: we know ht is valid due to H_DEREF, but ogl_tex_bind can
            // fail in debug builds if OglTex.id isn't a valid texture name)
            RETURN_STATUS_IF_ERR(ogl_tex_bind(ht, ot->tmu));
            int levels_to_skip;
            if(get_mipmaps(t, ot->state.filter, ot->q_flags, &levels_to_skip) < 0)
                // error => disable mipmapping
                ot->state.filter = GL_LINEAR;
            // (note: if first time, applies our defaults/previous overrides;
            // otherwise, replays all state changes)
            state_latch(&ot->state);
            upload_impl(t, ot->fmt, ot->int_fmt, levels_to_skip);
        }
        ogl_WarnIfError();

        ot->flags |= OT_IS_UPLOADED;

        // see rationale for <refs> at declaration of OglTex.
        // note: tex_free is safe even if this OglTex was wrapped -
        //       the Tex contains a mem handle.
        intptr_t refs = h_get_refcnt(ht);
        if(refs == 1)
        {
            // note: we verify above that OT_TEX_VALID is set
            tex_free(t);
            ot->flags &= ~OT_TEX_VALID;
        }
    }

    ot->flags |= OT_NEED_AUTO_UPLOAD;

    return INFO::OK;
}


//----------------------------------------------------------------------------
// getters
//----------------------------------------------------------------------------

// retrieve texture dimensions and bits per pixel.
// all params are optional and filled if non-NULL.
Status ogl_tex_get_size(Handle ht, size_t* w, size_t* h, size_t* bpp)
{
    H_DEREF(ht, OglTex, ot);

    if(w)
        *w = ot->t.w;
    if(h)
        *h = ot->t.h;
    if(bpp)
        *bpp = ot->t.bpp;
    return INFO::OK;
}


// retrieve TexFlags and the corresponding OpenGL format.
// the latter is determined during ogl_tex_upload and is 0 before that.
// all params are optional and filled if non-NULL.
Status ogl_tex_get_format(Handle ht, size_t* flags, GLenum* fmt)
{
    H_DEREF(ht, OglTex, ot);

    if(flags)
        *flags = ot->t.flags;
    if(fmt)
    {
        ENSURE(ot->flags & OT_IS_UPLOADED);
        *fmt = ot->fmt;
    }
    return INFO::OK;
}


// retrieve pointer to texel data.
//
// note: this memory is freed after a successful ogl_tex_upload for
// this texture. after that, the pointer we retrieve is NULL but
// the function doesn't fail (negative return value) by design.
// if you still need to get at the data, add a reference before
// uploading it or read directly from OpenGL (discouraged).
Status ogl_tex_get_data(Handle ht, u8** p)
{
    H_DEREF(ht, OglTex, ot);

    *p = tex_get_data(&ot->t);
    return INFO::OK;
}

// retrieve colour of 1x1 mipmap level
extern Status ogl_tex_get_average_colour(Handle ht, u32* p)
{
    H_DEREF(ht, OglTex, ot);
    warn_if_uploaded(ht, ot);

    *p = tex_get_average_colour(&ot->t);
    return INFO::OK;
}

//----------------------------------------------------------------------------
// misc API
//----------------------------------------------------------------------------

// bind the texture to the specified unit [number] in preparation for
// using it in rendering. if <ht> is 0, texturing is disabled instead.
//
// side effects:
// - changes the active texture unit;
// - (if return value is 0:) texturing was enabled/disabled on that unit.
//
// notes:
// - assumes multitexturing is available.
// - not necessary before calling ogl_tex_upload!
// - on error, the unit's texture state is unchanged; see implementation.
Status ogl_tex_bind(Handle ht, size_t unit)
{
    // note: there are many call sites of glActiveTextureARB, so caching
    // those and ignoring redundant sets isn't feasible.
    pglActiveTextureARB((int)(GL_TEXTURE0+unit));

    // special case: disable texturing
    if(ht == 0)
    {
        glDisable(GL_TEXTURE_2D);
        return INFO::OK;
    }

    // if this fails, the texture unit's state remains unchanged.
    // we don't bother catching that and disabling texturing because a
    // debug warning is raised anyway, and it's quite unlikely.
    H_DEREF(ht, OglTex, ot);
    ot->tmu = (u8)unit;

    // if 0, there's a problem in the OglTex reload/dtor logic.
    // binding it results in whiteness, which can have many causes;
    // we therefore complain so this one can be ruled out.
    ENSURE(ot->id != 0);

#if !CONFIG2_GLES
    glEnable(GL_TEXTURE_2D);
#endif
    glBindTexture(GL_TEXTURE_2D, ot->id);
    return INFO::OK;
}

Status ogl_tex_get_texture_id(Handle ht, GLuint* id)
{
    *id = 0;
    H_DEREF(ht, OglTex, ot);
    *id = ot->id;
    return INFO::OK;
}

// apply the specified transforms (as in tex_transform) to the image.
// must be called before uploading (raises a warning if called afterwards).
Status ogl_tex_transform(Handle ht, size_t transforms)
{
    H_DEREF(ht, OglTex, ot);
    Status ret = tex_transform(&ot->t, transforms);
    return ret;
}


// change the pixel format to that specified by <new_flags>.
// (note: this is equivalent to ogl_tex_transform(ht, ht_flags^new_flags).
Status ogl_tex_transform_to(Handle ht, size_t new_flags)
{
    H_DEREF(ht, OglTex, ot);
    Status ret = tex_transform_to(&ot->t, new_flags);
    return ret;
}


// return whether native S3TC support is available
bool ogl_tex_has_s3tc()
{
    // ogl_tex_upload must be called before this
    ENSURE(have_s3tc != -1);

    return (have_s3tc != 0);
}

// return whether anisotropic filtering support is available
bool ogl_tex_has_anisotropy()
{
    // ogl_tex_upload must be called before this
    ENSURE(have_anistropy != -1);

    return (have_anistropy != 0);
}