TexturedLineRData.cpp

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/* Copyright (C) 2012 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "precompiled.h"

#include "TexturedLineRData.h"

#include "graphics/Terrain.h"
#include "maths/MathUtil.h"
#include "maths/Quaternion.h"
#include "renderer/OverlayRenderer.h"
#include "renderer/Renderer.h"
#include "simulation2/Simulation2.h"
#include "simulation2/system/SimContext.h"
#include "simulation2/components/ICmpWaterManager.h"

/* Note: this implementation uses g_VBMan directly rather than access it through the nicer VertexArray interface,
 * because it allows you to work with variable amounts of vertices and indices more easily. New code should prefer
 * to use VertexArray where possible, though. */

void CTexturedLineRData::Render(const SOverlayTexturedLine& line, const CShaderProgramPtr& shader)
{
    if (!m_VB || !m_VBIndices)
        return; // might have failed to allocate

    // -- render main line quad strip ----------------------

    const int streamFlags = shader->GetStreamFlags();

    shader->BindTexture(str_baseTex, line.m_TextureBase->GetHandle());
    shader->BindTexture(str_maskTex, line.m_TextureMask->GetHandle());
    shader->Uniform(str_objectColor, line.m_Color);

    GLsizei stride = sizeof(CTexturedLineRData::SVertex);
    CTexturedLineRData::SVertex* vertexBase = reinterpret_cast<CTexturedLineRData::SVertex*>(m_VB->m_Owner->Bind());

    if (streamFlags & STREAM_POS)
        shader->VertexPointer(3, GL_FLOAT, stride, &vertexBase->m_Position[0]);

    if (streamFlags & STREAM_UV0)
        shader->TexCoordPointer(GL_TEXTURE0, 2, GL_FLOAT, stride, &vertexBase->m_UVs[0]);

    if (streamFlags & STREAM_UV1)
        shader->TexCoordPointer(GL_TEXTURE1, 2, GL_FLOAT, stride, &vertexBase->m_UVs[0]);

    u8* indexBase = m_VBIndices->m_Owner->Bind();

    shader->AssertPointersBound();
    glDrawElements(GL_TRIANGLES, m_VBIndices->m_Count, GL_UNSIGNED_SHORT, indexBase + sizeof(u16)*m_VBIndices->m_Index); 

    g_Renderer.GetStats().m_DrawCalls++;
    g_Renderer.GetStats().m_OverlayTris += m_VBIndices->m_Count/3; 
}

void CTexturedLineRData::Update(const SOverlayTexturedLine& line)
{
    if (m_VB)
    {
        g_VBMan.Release(m_VB);
        m_VB = NULL;
    }
    if (m_VBIndices)
    {
        g_VBMan.Release(m_VBIndices);
        m_VBIndices = NULL;
    }

    if (!line.m_SimContext)
    {
        debug_warn(L"[TexturedLineRData] No SimContext set for textured overlay line, cannot render (no terrain data)");
        return;
    }

    const CTerrain& terrain = line.m_SimContext->GetTerrain();
    CmpPtr<ICmpWaterManager> cmpWaterManager(*line.m_SimContext, SYSTEM_ENTITY);

    float v = 0.f;
    std::vector<SVertex> vertices;
    std::vector<u16> indices;

    size_t n = line.m_Coords.size() / 2; // number of line points
    bool closed = line.m_Closed;

    ENSURE(n >= 2); // minimum needed to avoid errors (also minimum value to make sense, can't draw a line between 1 point)

    // In each iteration, p1 is the position of vertex i, p0 is i-1, p2 is i+1.
    // To avoid slightly expensive terrain computations we cycle these around and
    // recompute p2 at the end of each iteration.

    CVector3D p0;
    CVector3D p1(line.m_Coords[0], 0, line.m_Coords[1]);
    CVector3D p2(line.m_Coords[(1 % n)*2], 0, line.m_Coords[(1 % n)*2+1]);

    if (closed)
        // grab the ending point so as to close the loop
        p0 = CVector3D(line.m_Coords[(n-1)*2], 0, line.m_Coords[(n-1)*2+1]);
    else
        // we don't want to loop around and use the direction towards the other end of the line, so create an artificial p0 that 
        // extends the p2 -> p1 direction, and use that point instead
        p0 = p1 + (p1 - p2);

    bool p1floating = false;
    bool p2floating = false;

    // Compute terrain heights, clamped to the water height (and remember whether
    // each point was floating on water, for normal computation later)

    // TODO: if we ever support more than one water level per map, recompute this per point
    float w = cmpWaterManager->GetExactWaterLevel(p0.X, p0.Z);

    p0.Y = terrain.GetExactGroundLevel(p0.X, p0.Z);
    if (p0.Y < w)
        p0.Y = w;

    p1.Y = terrain.GetExactGroundLevel(p1.X, p1.Z);
    if (p1.Y < w)
    {
        p1.Y = w;
        p1floating = true;
    }

    p2.Y = terrain.GetExactGroundLevel(p2.X, p2.Z);
    if (p2.Y < w)
    {
        p2.Y = w;
        p2floating = true;
    }

    for (size_t i = 0; i < n; ++i)
    {
        // For vertex i, compute bisector of lines (i-1)..(i) and (i)..(i+1)
        // perpendicular to terrain normal

        // Normal is vertical if on water, else computed from terrain
        CVector3D norm;
        if (p1floating)
            norm = CVector3D(0, 1, 0);
        else
            norm = terrain.CalcExactNormal(p1.X, p1.Z);

        CVector3D b = ((p1 - p0).Normalized() + (p2 - p1).Normalized()).Cross(norm);

        // Adjust bisector length to match the line thickness, along the line's width
        float l = b.Dot((p2 - p1).Normalized().Cross(norm));
        if (fabs(l) > 0.000001f) // avoid unlikely divide-by-zero
            b *= line.m_Thickness / l;

        // Push vertices and indices for each quad in GL_TRIANGLES order. The two triangles of each quad are indexed using
        // the winding orders (BR, BL, TR) and (TR, BL, TR) (where BR is bottom-right of this iteration's quad, TR top-right etc).
        SVertex vertex1(p1 + b + norm*OverlayRenderer::OVERLAY_VOFFSET, 0.f, v);
        SVertex vertex2(p1 - b + norm*OverlayRenderer::OVERLAY_VOFFSET, 1.f, v);
        vertices.push_back(vertex1);
        vertices.push_back(vertex2);

        u16 index1 = vertices.size() - 2; // index of vertex1 in this iteration (TR of this quad)
        u16 index2 = vertices.size() - 1; // index of the vertex2 in this iteration (TL of this quad)

        if (i == 0)
        {
            // initial two vertices to continue building triangles from (n must be >= 2 for this to work)
            indices.push_back(index1);
            indices.push_back(index2);
        }
        else 
        {
            u16 index1Prev = vertices.size() - 4; // index of the vertex1 in the previous iteration (BR of this quad)
            u16 index2Prev = vertices.size() - 3; // index of the vertex2 in the previous iteration (BL of this quad)
            ENSURE(index1Prev < vertices.size());
            ENSURE(index2Prev < vertices.size());
            // Add two corner points from last iteration and join with one of our own corners to create triangle 1
            // (don't need to do this if i == 1 because i == 0 are the first two ones, they don't need to be copied)
            if (i > 1)
            {
                indices.push_back(index1Prev);
                indices.push_back(index2Prev);
            }
            indices.push_back(index1); // complete triangle 1

            // create triangle 2, specifying the adjacent side's vertices in the opposite order from triangle 1
            indices.push_back(index1);
            indices.push_back(index2Prev);
            indices.push_back(index2);
        }

        // alternate V coordinate for debugging
        v = 1 - v;

        // cycle the p's and compute the new p2
        p0 = p1;
        p1 = p2;
        p1floating = p2floating;

        // if in closed mode, wrap around the coordinate array for p2 -- otherwise, extend linearly
        if (!closed && i == n-2)
            // next iteration is the last point of the line, so create an artificial p2 that extends the p0 -> p1 direction
            p2 = p1 + (p1 - p0);
        else
            p2 = CVector3D(line.m_Coords[((i+2) % n)*2], 0, line.m_Coords[((i+2) % n)*2+1]);

        p2.Y = terrain.GetExactGroundLevel(p2.X, p2.Z);
        if (p2.Y < w)
        {
            p2.Y = w;
            p2floating = true;
        }
        else
            p2floating = false;
    }

    if (closed)
    {
        // close the path
        indices.push_back(vertices.size()-2);
        indices.push_back(vertices.size()-1);
        indices.push_back(0);

        indices.push_back(0);
        indices.push_back(vertices.size()-1);
        indices.push_back(1);
    }
    else
    {
        // Create start and end caps. On either end, this is done by taking the centroid between the last and second-to-last pair of
        // vertices that was generated along the path (i.e. the vertex1's and vertex2's from above), taking a directional vector 
        // between them, and drawing the line cap in the plane given by the two butt-end corner points plus said vector.
        std::vector<u16> capIndices;
        std::vector<SVertex> capVertices;

        // create end cap
        CreateLineCap(
            line,
            // the order of these vertices is important here, swapping them produces caps at the wrong side
            vertices[vertices.size()-2].m_Position, // top-right vertex of last quad
            vertices[vertices.size()-1].m_Position, // top-left vertex of last quad
            // directional vector between centroids of last vertex pair and second-to-last vertex pair
            (Centroid(vertices[vertices.size()-2], vertices[vertices.size()-1]) - Centroid(vertices[vertices.size()-4], vertices[vertices.size()-3])).Normalized(),
            line.m_EndCapType,
            capVertices,
            capIndices
        );

        for (unsigned i = 0; i < capIndices.size(); i++)
            capIndices[i] += vertices.size();

        vertices.insert(vertices.end(), capVertices.begin(), capVertices.end());
        indices.insert(indices.end(), capIndices.begin(), capIndices.end());

        capIndices.clear();
        capVertices.clear();

        // create start cap
        CreateLineCap(
            line,
            // the order of these vertices is important here, swapping them produces caps at the wrong side
            vertices[1].m_Position,
            vertices[0].m_Position,
            // directional vector between centroids of first vertex pair and second vertex pair
            (Centroid(vertices[1], vertices[0]) - Centroid(vertices[3], vertices[2])).Normalized(),
            line.m_StartCapType,
            capVertices,
            capIndices
        );

        for (unsigned i = 0; i < capIndices.size(); i++)
            capIndices[i] += vertices.size();

        vertices.insert(vertices.end(), capVertices.begin(), capVertices.end());
        indices.insert(indices.end(), capIndices.begin(), capIndices.end());
    }

    ENSURE(indices.size() % 3 == 0); // GL_TRIANGLES indices, so must be multiple of 3

    m_VB = g_VBMan.Allocate(sizeof(SVertex), vertices.size(), GL_STATIC_DRAW, GL_ARRAY_BUFFER);
    if (m_VB) // allocation might fail (e.g. due to too many vertices)
    {
        m_VB->m_Owner->UpdateChunkVertices(m_VB, &vertices[0]); // copy data into VBO

        for (size_t k = 0; k < indices.size(); ++k)
            indices[k] += m_VB->m_Index;

        m_VBIndices = g_VBMan.Allocate(sizeof(u16), indices.size(), GL_STATIC_DRAW, GL_ELEMENT_ARRAY_BUFFER);
        if (m_VBIndices)
            m_VBIndices->m_Owner->UpdateChunkVertices(m_VBIndices, &indices[0]);
    }

}

void CTexturedLineRData::CreateLineCap(const SOverlayTexturedLine& line, const CVector3D& corner1, const CVector3D& corner2,
    const CVector3D& lineDirectionNormal, SOverlayTexturedLine::LineCapType endCapType, std::vector<SVertex>& verticesOut,
    std::vector<u16>& indicesOut)
{
    if (endCapType == SOverlayTexturedLine::LINECAP_FLAT)
        return; // no action needed, this is the default

    // When not in closed mode, we've created artificial points for the start- and endpoints that extend the line in the
    // direction of the first and the last segment, respectively. Thus, we know both the start and endpoints have perpendicular
    // butt endings, i.e. the end corner vertices on either side of the line extend perpendicularly from the segment direction.
    // That is to say, when viewed from the top, we will have something like
    //                                                 .
    //  this:                     and not like this:  /|
    //         ----+                                 / |
    //             |                                /  .
    //             |                                  /
    //         ----+                                 /
    //

    int roundCapPoints = 8; // amount of points to sample along the semicircle for rounded caps (including corner points)
    float radius = line.m_Thickness;

    CVector3D centerPoint = (corner1 + corner2) * 0.5f;
    SVertex centerVertex(centerPoint, 0.5f, 0.5f);
    u16 indexOffset = verticesOut.size(); // index offset in verticesOut from where we start adding our vertices

    switch (endCapType)
    {
    case SOverlayTexturedLine::LINECAP_SHARP:
        {
            roundCapPoints = 3; // creates only one point directly ahead
            radius *= 1.5f; // make it a bit sharper (note that we don't use the radius for the butt-end corner points so it should be ok)
            centerVertex.m_UVs[0] = 0.480f; // slight visual correction to make the texture match up better at the corner points
        }
        // fall-through
    case SOverlayTexturedLine::LINECAP_ROUND:
        {
            // Draw a rounded line cap in the 3D plane of the line specified by the two corner points and the normal vector of the 
            // line's direction. The terrain normal at the centroid between the two corner points is perpendicular to this plane.
            // The way this works is by taking a vector from the corner points' centroid to one of the corner points (which is then 
            // of radius length), and rotate it around the terrain normal vector in that centroid. This will rotate the vector in 
            // the line's plane, producing the desired rounded cap.

            // To please OpenGL's winding order, this angle needs to be negated depending on whether we start rotating from 
            // the (center -> corner1) or (center -> corner2) vector. For the (center -> corner2) vector, we apparently need to use 
            // the negated angle.
            float stepAngle = -(float)(M_PI/(roundCapPoints-1));

            // Push the vertices in triangle fan order (easy to generate GL_TRIANGLES indices for afterwards)
            // Note that we're manually adding the corner vertices instead of having them be generated by the rotating vector. 
            // This is because we want to support an overly large radius to make the sharp line ending look sharper.
            verticesOut.push_back(centerVertex); 
            verticesOut.push_back(SVertex(corner2, 0.f, 0.f));

            // Get the base vector that we will incrementally rotate in the cap plane to produce the radial sample points.
            // Normally corner2 - centerPoint would suffice for this since it is of radius length, but we want to support custom 
            // radii to support tuning the 'sharpness' of sharp end caps (see above)
            CVector3D rotationBaseVector = (corner2 - centerPoint).Normalized() * radius;
            // Calculate the normal vector of the plane in which we're going to be drawing the line cap. This is the vector that
            // is perpendicular to both baseVector and the 'lineDirectionNormal' vector indicating the direction of the line.
            // Note that we shouldn't use terrain->CalcExactNormal() here because if the line is being rendered on top of water,
            // then CalcExactNormal will return the normal vector of the terrain that's underwater (which can be quite funky).
            CVector3D capPlaneNormal = lineDirectionNormal.Cross(rotationBaseVector).Normalized();

            for (int i = 1; i < roundCapPoints - 1; ++i)
            {
                // Rotate the centerPoint -> corner vector by i*stepAngle radians around the cap plane normal at the center point.
                CQuaternion quatRotation;
                quatRotation.FromAxisAngle(capPlaneNormal, i * stepAngle);
                CVector3D worldPos3D = centerPoint + quatRotation.Rotate(rotationBaseVector);

                // Let v range from 0 to 1 as we move along the semi-circle, keep u fixed at 0 (i.e. curve the left vertical edge 
                // of the texture around the edge of the semicircle)
                float u = 0.f;
                float v = clamp((i/(float)(roundCapPoints-1)), 0.f, 1.f); // pos, u, v
                verticesOut.push_back(SVertex(worldPos3D, u, v));
            }

            // connect back to the other butt-end corner point to complete the semicircle 
            verticesOut.push_back(SVertex(corner1, 0.f, 1.f)); 

            // now push indices in GL_TRIANGLES order; vertices[indexOffset] is the center vertex, vertices[indexOffset + 1] is the 
            // first corner point, then a bunch of radial samples, and then at the end we have the other corner point again. So: 
            for (int i=1; i < roundCapPoints; ++i)
            {
                indicesOut.push_back(indexOffset); // center vertex 
                indicesOut.push_back(indexOffset + i); 
                indicesOut.push_back(indexOffset + i + 1); 
            }
        }
        break;

    case SOverlayTexturedLine::LINECAP_SQUARE:
        {
            // Extend the (corner1 -> corner2) vector along the direction normal and draw a square line ending consisting of 
            // three triangles (sort of like a triangle fan)
            // NOTE: The order in which the vertices are pushed out determines the visibility, as they
            // are rendered only one-sided; the wrong order of vertices will make the cap visible only from the bottom.
            verticesOut.push_back(centerVertex);
            verticesOut.push_back(SVertex(corner2, 0.f, 0.f));
            verticesOut.push_back(SVertex(corner2 + (lineDirectionNormal * (line.m_Thickness)), 0.f, 0.33333f)); // extend butt corner point 2 along the normal vector 
            verticesOut.push_back(SVertex(corner1 + (lineDirectionNormal * (line.m_Thickness)), 0.f, 0.66666f)); // extend butt corner point 1 along the normal vector 
            verticesOut.push_back(SVertex(corner1, 0.f, 1.0f)); // push butt corner point 1 

            for (int i=1; i < 4; ++i) 
            { 
                indicesOut.push_back(indexOffset); // center point 
                indicesOut.push_back(indexOffset + i); 
                indicesOut.push_back(indexOffset + i + 1);
            } 
        }
        break;

    default:
        break;
    }

}