AtomicGameEngine/Source/AtomicGlow/Kernel/Raster.cpp

#include "Raster.h"

#ifdef ATOMIC_PLATFORM_WINDOWS
#include <float.h>
#endif

namespace AtomicGlow
{

namespace
{

/// Return the maximum of the two arguments. For floating point values, it returns the second value if the first is NaN.
template <typename T>
inline const T & _max(const T & a, const T & b)
{
    return (b < a) ? a : b;
}

/// Return the maximum of the three arguments.
template <typename T>
inline const T & _max3(const T & a, const T & b, const T & c)
{
    return _max(a, _max(b, c));
}

/// Return the minimum of two values.
template <typename T>
inline const T & _min(const T & a, const T & b)
{
    return (a < b) ? a : b;
}

/// Return the maximum of the three arguments.
template <typename T>
inline const T & _min3(const T & a, const T & b, const T & c)
{
    return _min(a, _min(b, c));
}

/// Clamp between two values.
template <typename T>
inline const T & _clamp(const T & x, const T & a, const T & b)
{
    return _min(_max(x, a), b);
}

inline bool isFinite(const float f)
{

#ifdef ATOMIC_PLATFORM_WINDOWS
    return _finite(f) != 0;
#endif

#ifdef ATOMIC_PLATFORM_OSX
    return isfinite(f);
#endif

#ifdef ATOMIC_PLATFORM_LINUX
    return finitef(f);
#endif

}

static inline float delta(float bot, float top, float ih)
{
    return (bot - top) * ih;
}

static inline Vector2 delta(const Vector2& bot, const Vector2& top, float ih)
{
    return (bot - top) * ih;
}

static inline Vector3 delta(const Vector3& bot, const Vector3& top, float ih)
{
    return (bot - top) * ih;
}

// @@ The implementation in nvmath.h should be equivalent.
static inline int iround(float f)
{
    // @@ Optimize this.
    return int(floorf(f+0.5f));
    //return int(round(f));
    //return int(f);
}


class ClippedTriangle
{
public:
    ClippedTriangle(const Vector2& a, const Vector2& b, const Vector2& c)
    {
        m_numVertices = 3;
        m_activeVertexBuffer = 0;

        m_verticesA[0]=a;
        m_verticesA[1]=b;
        m_verticesA[2]=c;

        m_vertexBuffers[0] = m_verticesA;
        m_vertexBuffers[1] = m_verticesB;
    }

    unsigned vertexCount()
    {
        return m_numVertices;
    }

    const Vector2 * vertices()
    {
        return m_vertexBuffers[m_activeVertexBuffer];
    }

    inline void clipHorizontalPlane(float offset, float clipdirection)
    {
        Vector2 * v  = m_vertexBuffers[m_activeVertexBuffer];
        m_activeVertexBuffer ^= 1;
        Vector2 * v2 = m_vertexBuffers[m_activeVertexBuffer];

        v[m_numVertices] = v[0];

        float dy2,   dy1 = offset - v[0].y_;
        int   dy2in, dy1in = clipdirection*dy1 >= 0;
        unsigned  p=0;

        for (unsigned k=0; k<m_numVertices; k++)
        {
            dy2   = offset - v[k+1].y_;
            dy2in = clipdirection*dy2 >= 0;

            if (dy1in) v2[p++] = v[k];

            if ( dy1in + dy2in == 1 ) // not both in/out
            {
                float dx = v[k+1].x_ - v[k].x_;
                float dy = v[k+1].y_ - v[k].y_;
                v2[p++] = Vector2(v[k].x_ + dy1*(dx/dy), offset);
            }

            dy1 = dy2; dy1in = dy2in;
        }
        m_numVertices = p;

        //for (uint k=0; k<m_numVertices; k++) printf("(%f, %f)\n", v2[k].x, v2[k].y); printf("\n");
    }

    inline void clipVerticalPlane(float offset, float clipdirection )
    {
        Vector2 * v  = m_vertexBuffers[m_activeVertexBuffer];
        m_activeVertexBuffer ^= 1;
        Vector2 * v2 = m_vertexBuffers[m_activeVertexBuffer];

        v[m_numVertices] = v[0];

        float dx2,   dx1   = offset - v[0].x_;
        int   dx2in, dx1in = clipdirection*dx1 >= 0;
        unsigned  p=0;

        for (unsigned k=0; k<m_numVertices; k++)
        {
            dx2 = offset - v[k+1].x_;
            dx2in = clipdirection*dx2 >= 0;

            if (dx1in) v2[p++] = v[k];

            if ( dx1in + dx2in == 1 ) // not both in/out
            {
                float dx = v[k+1].x_ - v[k].x_;
                float dy = v[k+1].y_ - v[k].y_;
                v2[p++] = Vector2(offset, v[k].y_ + dx1*(dy/dx));
            }

            dx1 = dx2; dx1in = dx2in;
        }
        m_numVertices = p;

        //for (uint k=0; k<m_numVertices; k++) printf("(%f, %f)\n", v2[k].x, v2[k].y); printf("\n");
    }

    void computeAreaCentroid()
    {
        Vector2 * v  = m_vertexBuffers[m_activeVertexBuffer];
        v[m_numVertices] = v[0];

        m_area = 0;
        float centroidx=0, centroidy=0;
        for (unsigned k=0; k<m_numVertices; k++)
        {
            // http://local.wasp.uwa.edu.au/~pbourke/geometry/polyarea/
            float f = v[k].x_*v[k+1].y_ - v[k+1].x_*v[k].y_;
            m_area += f;
            centroidx += f * (v[k].x_ + v[k+1].x_);
            centroidy += f * (v[k].y_ + v[k+1].y_);
        }
        m_area = 0.5f * fabs(m_area);
        if (m_area==0) {
            m_centroid = Vector2(0.0f, 0.0f);
        } else {
            m_centroid = Vector2(centroidx/(6*m_area), centroidy/(6*m_area));
        }
    }

    void clipAABox(float x0, float y0, float x1, float y1)
    {
        clipVerticalPlane  ( x0, -1);
        clipHorizontalPlane( y0, -1);
        clipVerticalPlane  ( x1,  1);
        clipHorizontalPlane( y1,  1);

        computeAreaCentroid();
    }

    Vector2 centroid()
    {
        return m_centroid;
    }

    float area()
    {
        return m_area;
    }

private:
    Vector2 m_verticesA[7+1];
    Vector2 m_verticesB[7+1];
    Vector2 * m_vertexBuffers[2];
    unsigned    m_numVertices;
    unsigned    m_activeVertexBuffer;
    float   m_area;
    Vector2 m_centroid;
};


/// A triangle vertex.
struct Vertex
{
    Vector2 pos;	// Position.
    Vector3 tex;	// Texcoord. (Barycentric coordinate)
};


/// A triangle for rasterization.
struct Triangle
{
    Triangle(const Vector2& v0, const Vector2& v1, const Vector2& v2, const Vector3& t0, const Vector3& t1, const Vector3& t2);

    bool computeDeltas();

    bool draw(const Vector2& extents, bool enableScissors, RasterSamplingCallback cb, void *param);
    bool drawAA(const Vector2& extents, bool enableScissors, RasterSamplingCallback cb, void *param);

    void flipBackface();
    void computeUnitInwardNormals();

    // Vertices.
    Vector2 v1, v2, v3;
    Vector2 n1, n2, n3; // unit inward normals
    Vector3 t1, t2, t3;

    // Deltas.
    Vector3 dx, dy;

    float sign;
    bool valid;
};


/// Triangle ctor.
Triangle::Triangle(const Vector2& v0, const Vector2& v1, const Vector2& v2, const Vector3& t0, const Vector3& t1, const Vector3& t2)
{
    // Init vertices.
    this->v1 = v0;
    this->v2 = v2;
    this->v3 = v1;

    // Set barycentric coordinates.
    this->t1 = t0;
    this->t2 = t2;
    this->t3 = t1;

    // make sure every triangle is front facing.
    flipBackface();

    // Compute deltas.
    valid = computeDeltas();

    computeUnitInwardNormals();
}


/// Compute texture space deltas.
/// This method takes two edge vectors that form a basis, determines the
/// coordinates of the canonic vectors in that basis, and computes the
/// texture gradient that corresponds to those vectors.
bool Triangle::computeDeltas()
{
    Vector2 e0 = v3 - v1;
    Vector2 e1 = v2 - v1;

    Vector3 de0 = t3 - t1;
    Vector3 de1 = t2 - t1;

    float denom = 1.0f / (e0.y_ * e1.x_ - e1.y_ * e0.x_);
    if (!isFinite(denom)) {
        return false;
    }

    float lambda1 = - e1.y_ * denom;
    float lambda2 = e0.y_ * denom;
    float lambda3 = e1.x_ * denom;
    float lambda4 = - e0.x_ * denom;

    dx = de0 * lambda1 + de1 * lambda2;
    dy = de0 * lambda3 + de1 * lambda4;

    return true;
}

// compute unit inward normals for each edge.
void Triangle::computeUnitInwardNormals()
{
    n1 = v1 - v2; n1 = Vector2(-n1.y_, n1.x_); n1 = n1 * (1.0f/sqrtf(n1.x_*n1.x_ + n1.y_*n1.y_));
    n2 = v2 - v3; n2 = Vector2(-n2.y_, n2.x_); n2 = n2 * (1.0f/sqrtf(n2.x_*n2.x_ + n2.y_*n2.y_));
    n3 = v3 - v1; n3 = Vector2(-n3.y_, n3.x_); n3 = n3 * (1.0f/sqrtf(n3.x_*n3.x_ + n3.y_*n3.y_));
}

void Triangle::flipBackface()
{
    // check if triangle is backfacing, if so, swap two vertices
    if ( ((v3.x_-v1.x_)*(v2.y_-v1.y_) - (v3.y_-v1.y_)*(v2.x_-v1.x_)) < 0 ) {
        Vector2 hv=v1; v1=v2; v2=hv; // swap pos
        Vector3 ht=t1; t1=t2; t2=ht; // swap tex
    }
}

bool Triangle::draw(const Vector2 & extents, bool enableScissors, RasterSamplingCallback cb, void * param)
{
    // 28.4 fixed-point coordinates
    const int Y1 = iround(16.0f * v1.y_);
    const int Y2 = iround(16.0f * v2.y_);
    const int Y3 = iround(16.0f * v3.y_);

    const int X1 = iround(16.0f * v1.x_);
    const int X2 = iround(16.0f * v2.x_);
    const int X3 = iround(16.0f * v3.x_);

    // Deltas
    const int DX12 = X1 - X2;
    const int DX23 = X2 - X3;
    const int DX31 = X3 - X1;

    const int DY12 = Y1 - Y2;
    const int DY23 = Y2 - Y3;
    const int DY31 = Y3 - Y1;

    // Fixed-point deltas
    const int FDX12 = DX12 << 4;
    const int FDX23 = DX23 << 4;
    const int FDX31 = DX31 << 4;

    const int FDY12 = DY12 << 4;
    const int FDY23 = DY23 << 4;
    const int FDY31 = DY31 << 4;

    int minx, miny, maxx, maxy;
    if (enableScissors) {
        int frustumX0 =  0 << 4;
        int frustumY0 =  0 << 4;
        int frustumX1 =  (int)extents.x_ << 4;
        int frustumY1 =  (int)extents.y_ << 4;

        // Bounding rectangle
        minx = (_max(_min3(X1, X2, X3), frustumX0) + 0xF) >> 4;
        miny = (_max(_min3(Y1, Y2, Y3), frustumY0) + 0xF) >> 4;
        maxx = (_min(_max3(X1, X2, X3), frustumX1) + 0xF) >> 4;
        maxy = (_min(_max3(Y1, Y2, Y3), frustumY1) + 0xF) >> 4;
    }
    else {
        // Bounding rectangle
        minx = (_min3(X1, X2, X3) + 0xF) >> 4;
        miny = (_min3(Y1, Y2, Y3) + 0xF) >> 4;
        maxx = (_max3(X1, X2, X3) + 0xF) >> 4;
        maxy = (_max3(Y1, Y2, Y3) + 0xF) >> 4;
    }

    // Block size, standard 8x8 (must be power of two)
    const int q = 8;

    // @@ This won't work when minx,miny are negative. This code path is not used. Leaving as is for now.
    assert(minx >= 0);
    assert(miny >= 0);

    // Start in corner of 8x8 block
    minx &= ~(q - 1);
    miny &= ~(q - 1);

    // Half-edge constants
    int C1 = DY12 * X1 - DX12 * Y1;
    int C2 = DY23 * X2 - DX23 * Y2;
    int C3 = DY31 * X3 - DX31 * Y3;

    // Correct for fill convention
    if(DY12 < 0 || (DY12 == 0 && DX12 > 0)) C1++;
    if(DY23 < 0 || (DY23 == 0 && DX23 > 0)) C2++;
    if(DY31 < 0 || (DY31 == 0 && DX31 > 0)) C3++;

    // Loop through blocks
    for(int y = miny; y < maxy; y += q)
    {
        for(int x = minx; x < maxx; x += q)
        {
            // Corners of block
            int x0 = x << 4;
            int x1 = (x + q - 1) << 4;
            int y0 = y << 4;
            int y1 = (y + q - 1) << 4;

            // Evaluate half-space functions
            bool a00 = C1 + DX12 * y0 - DY12 * x0 > 0;
            bool a10 = C1 + DX12 * y0 - DY12 * x1 > 0;
            bool a01 = C1 + DX12 * y1 - DY12 * x0 > 0;
            bool a11 = C1 + DX12 * y1 - DY12 * x1 > 0;
            int a = (a00 << 0) | (a10 << 1) | (a01 << 2) | (a11 << 3);

            bool b00 = C2 + DX23 * y0 - DY23 * x0 > 0;
            bool b10 = C2 + DX23 * y0 - DY23 * x1 > 0;
            bool b01 = C2 + DX23 * y1 - DY23 * x0 > 0;
            bool b11 = C2 + DX23 * y1 - DY23 * x1 > 0;
            int b = (b00 << 0) | (b10 << 1) | (b01 << 2) | (b11 << 3);

            bool c00 = C3 + DX31 * y0 - DY31 * x0 > 0;
            bool c10 = C3 + DX31 * y0 - DY31 * x1 > 0;
            bool c01 = C3 + DX31 * y1 - DY31 * x0 > 0;
            bool c11 = C3 + DX31 * y1 - DY31 * x1 > 0;
            int c = (c00 << 0) | (c10 << 1) | (c01 << 2) | (c11 << 3);

            // Skip block when outside an edge
            if(a == 0x0 || b == 0x0 || c == 0x0) continue;

            // Accept whole block when totally covered
            if(a == 0xF && b == 0xF && c == 0xF)
            {
                Vector3 texRow = t1 + dy*(y0 - v1.y_) + dx*(x0 - v1.x_);

                for(int iy = y; iy < y + q; iy++)
                {
                    Vector3 tex = texRow;
                    for(int ix = x; ix < x + q; ix++)
                    {
                        Vector3 tex2 = t1 + dx * (ix - v1.x_) + dy * (iy - v1.y_);
                        if (!cb(param, ix, iy, tex2, dx, dy, 1.0)) {
                            // early out.
                            return false;
                        }
                        tex += dx;
                    }
                    texRow += dy;
                }
            }
            else // Partially covered block
            {
                int CY1 = C1 + DX12 * y0 - DY12 * x0;
                int CY2 = C2 + DX23 * y0 - DY23 * x0;
                int CY3 = C3 + DX31 * y0 - DY31 * x0;
                Vector3 texRow = t1 + dy*(y0 - v1.y_) + dx*(x0 - v1.x_);

                for(int iy = y; iy < y + q; iy++)
                {
                    int CX1 = CY1;
                    int CX2 = CY2;
                    int CX3 = CY3;
                    Vector3 tex = texRow;

                    for(int ix = x; ix < x + q; ix++)
                    {
                        if(CX1 > 0 && CX2 > 0 && CX3 > 0)
                        {
                            Vector3 tex2 = t1 + dx * (ix - v1.x_) + dy * (iy - v1.y_);
                            if (!cb(param, ix, iy, tex2, dx, dy, 1.0))
                            {
                                // early out.
                                return false;
                            }
                        }

                        CX1 -= FDY12;
                        CX2 -= FDY23;
                        CX3 -= FDY31;
                        tex += dx;
                    }

                    CY1 += FDX12;
                    CY2 += FDX23;
                    CY3 += FDX31;
                    texRow += dy;
                }
            }
        }
    }

    return true;
}


#define PX_INSIDE    1.0f/sqrt(2.0f)
#define PX_OUTSIDE  -1.0f/sqrt(2.0f)

#define BK_SIZE 8
#define BK_INSIDE   sqrt(BK_SIZE*BK_SIZE/2.0f)
#define BK_OUTSIDE -sqrt(BK_SIZE*BK_SIZE/2.0f)

// extents has to be multiple of BK_SIZE!!
bool Triangle::drawAA(const Vector2& extents, bool enableScissors, RasterSamplingCallback cb, void * param)
{
    float minx, miny, maxx, maxy;
    if (enableScissors) {
        // Bounding rectangle
        minx = floorf(_max(_min3(v1.x_, v2.x_, v3.x_), 0.0f));
        miny = floorf(_max(_min3(v1.y_, v2.y_, v3.y_), 0.0f));
        maxx = ceilf( _min(_max3(v1.x_, v2.x_, v3.x_), extents.x_-1.0f));
        maxy = ceilf( _min(_max3(v1.y_, v2.y_, v3.y_), extents.y_-1.0f));
    }
    else {
        // Bounding rectangle
        minx = floorf(_min3(v1.x_, v2.x_, v3.x_));
        miny = floorf(_min3(v1.y_, v2.y_, v3.y_));
        maxx = ceilf( _max3(v1.x_, v2.x_, v3.x_));
        maxy = ceilf( _max3(v1.y_, v2.y_, v3.y_));
    }

    // There's no reason to align the blocks to the viewport, instead we align them to the origin of the triangle bounds.
    minx = floorf(minx);
    miny = floorf(miny);
    //minx = (float)(((int)minx) & (~((int)BK_SIZE - 1))); // align to blocksize (we don't need to worry about blocks partially out of viewport)
    //miny = (float)(((int)miny) & (~((int)BK_SIZE - 1)));

    minx += 0.5; miny +=0.5;  // sampling at texel centers!
    maxx += 0.5; maxy +=0.5;

    // Half-edge constants
    float C1 = n1.x_ * (-v1.x_) + n1.y_ * (-v1.y_);
    float C2 = n2.x_ * (-v2.x_) + n2.y_ * (-v2.y_);
    float C3 = n3.x_ * (-v3.x_) + n3.y_ * (-v3.y_);

    // Loop through blocks
    for(float y0 = miny; y0 <= maxy; y0 += BK_SIZE)
    {
        for(float x0 = minx; x0 <= maxx; x0 += BK_SIZE)
        {
            // Corners of block
            float xc = (x0 + (BK_SIZE-1)/2.0f);
            float yc = (y0 + (BK_SIZE-1)/2.0f);

            // Evaluate half-space functions
            float aC = C1 + n1.x_ * xc + n1.y_ * yc;
            float bC = C2 + n2.x_ * xc + n2.y_ * yc;
            float cC = C3 + n3.x_ * xc + n3.y_ * yc;

            // Skip block when outside an edge
            if( (aC <= BK_OUTSIDE) || (bC <= BK_OUTSIDE) || (cC <= BK_OUTSIDE) ) continue;

            // Accept whole block when totally covered
            if( (aC >= BK_INSIDE) && (bC >= BK_INSIDE) && (cC >= BK_INSIDE) )
            {
                Vector3 texRow = t1 + dy*(y0 - v1.y_) + dx*(x0 - v1.x_);

                for (float y = y0; y < y0 + BK_SIZE; y++)
                {
                    Vector3 tex = texRow;
                    for(float x = x0; x < x0 + BK_SIZE; x++)
                    {
                        if (!cb(param, (int)x, (int)y, tex, dx, dy, 1.0f))
                        {
                            return false;
                        }
                        tex += dx;
                    }
                    texRow += dy;
                }
            }
            else // Partially covered block
            {
                float CY1 = C1 + n1.x_ * x0 + n1.y_ * y0;
                float CY2 = C2 + n2.x_ * x0 + n2.y_ * y0;
                float CY3 = C3 + n3.x_ * x0 + n3.y_ * y0;
                Vector3 texRow = t1 + dy*(y0 - v1.y_) + dx*(x0 - v1.x_);

                for(float y = y0; y < y0 + BK_SIZE; y++)
                {
                    float CX1 = CY1;
                    float CX2 = CY2;
                    float CX3 = CY3;
                    Vector3 tex = texRow;

                    for (float x = x0; x < x0 + BK_SIZE; x++)
                    {
                        if (CX1 >= PX_INSIDE && CX2 >= PX_INSIDE && CX3 >= PX_INSIDE)
                        {
                            // pixel completely covered
                            Vector3 tex = t1 + dx * (x - v1.x_) + dy * (y - v1.y_);
                            if (!cb(param, (int)x, (int)y, tex, dx, dy, 1.0f))
                            {
                                return false;
                            }
                        }
                        else if ((CX1 >= PX_OUTSIDE) && (CX2 >= PX_OUTSIDE) && (CX3 >= PX_OUTSIDE))
                        {
                            // triangle partially covers pixel. do clipping.
                            ClippedTriangle ct(v1-Vector2(x,y), v2-Vector2(x,y), v3-Vector2(x,y));
                            ct.clipAABox(-0.5, -0.5, 0.5, 0.5);
                            Vector2 centroid = ct.centroid();
                            float area = ct.area();
                            if (area > 0.0f)
                            {
                                Vector3 texCent = tex - dx*centroid.x_ - dy*centroid.y_;
                                //nvCheck(texCent.x_ >= -0.1f && texCent.x_ <= 1.1f); // @@ Centroid is not very exact...
                                //nvCheck(texCent.y_ >= -0.1f && texCent.y_ <= 1.1f);
                                //nvCheck(texCent.z >= -0.1f && texCent.z <= 1.1f);
                                //Vector3 texCent2 = t1 + dx * (x - v1.x_) + dy * (y - v1.y_);
                                if (!cb(param, (int)x, (int)y, texCent, dx, dy, area))
                                {
                                    return false;
                                }
                            }
                        }

                        CX1 += n1.x_;
                        CX2 += n2.x_;
                        CX3 += n3.x_;
                        tex += dx;
                    }

                    CY1 += n1.y_;
                    CY2 += n2.y_;
                    CY3 += n3.y_;
                    texRow += dy;
                }
            }
        }
    }

    return true;
}

} // namespace


/// Process the given triangle.
bool Raster::DrawTriangle(bool antialias, const Vector2& extents, bool enableScissors, const Vector2 v[3], RasterSamplingCallback cb, void* param)
{
    Triangle tri(v[0], v[1], v[2], Vector3(1, 0, 0), Vector3(0, 1, 0), Vector3(0, 0, 1));

    if (tri.valid) {
        if (antialias) {
            return tri.drawAA(extents, enableScissors, cb, param);
        } else {
            return tri.draw(extents, enableScissors, cb, param);
        }
    }

    return true;
}

inline float triangleArea(const Vector2& v1, const Vector2& v2, const Vector2& v3)
{
    return 0.5f * (v3.x_ * v1.y_ + v1.x_ * v2.y_ + v2.x_ * v3.y_ - v2.x_ * v1.y_ - v3.x_ * v2.y_ - v1.x_ * v3.y_);
}

/// Process the given quad.
bool Raster::DrawQuad(bool antialias, const Vector2& extents, bool enableScissors, const Vector2 v[4], RasterSamplingCallback cb, void * param)
{
    bool sign0 = triangleArea(v[0], v[1], v[2]) > 0.0f;
    bool sign1 = triangleArea(v[0], v[2], v[3]) > 0.0f;

    // Divide the quad into two non overlapping triangles.
    if (sign0 == sign1) {
        Triangle tri0(v[0], v[1], v[2], Vector3(0,0,0), Vector3(1,0,0), Vector3(1,1,0));
        Triangle tri1(v[0], v[2], v[3], Vector3(0,0,0), Vector3(1,1,0), Vector3(0,1,0));

        if (tri0.valid && tri1.valid) {
            if (antialias) {
                return tri0.drawAA(extents, enableScissors, cb, param) && tri1.drawAA(extents, enableScissors, cb, param);
            } else {
                return tri0.draw(extents, enableScissors, cb, param) && tri1.draw(extents, enableScissors, cb, param);
            }
        }
    }
    else
    {
        Triangle tri0(v[0], v[1], v[3], Vector3(0,0,0), Vector3(1,0,0), Vector3(0,1,0));
        Triangle tri1(v[1], v[2], v[3], Vector3(1,0,0), Vector3(1,1,0), Vector3(0,1,0));

        if (tri0.valid && tri1.valid) {
            if (antialias) {
                return tri0.drawAA(extents, enableScissors, cb, param) && tri1.drawAA(extents, enableScissors, cb, param);
            } else {
                return tri0.draw(extents, enableScissors, cb, param) && tri1.draw(extents, enableScissors, cb, param);
            }
        }
    }

    return true;
}

}