Triangle Raster Function

triangle.cpp

void DrawTriangleTextured(SDL_Surface *Buffer,SDL_Surface *Texture,float * Zbuffer, vec3 *Points,vec2 *UV,float* Intensity) { 
    
    Uint32 Rshift = 16, Gshift =8, Bshift = 0, Ashift=24;
    vec2 BBoxmin = {};
    vec2 BBoxmax = {};
    // Compute triangle bounding box
    BBoxmin.X = MIN(MIN(Points[0].X, Points[1].X), Points[2].X);
    BBoxmin.Y = MIN(MIN(Points[0].Y, Points[1].Y), Points[2].Y);
    BBoxmax.X = MAX(MAX(Points[0].X, Points[1].X), Points[2].X);
    BBoxmax.Y = MAX(MAX(Points[0].Y, Points[1].Y), Points[2].Y);

    // Clip against screen bounds
   BBoxmin.X = MAX(BBoxmin.X, 0);
   BBoxmin.Y = MAX(BBoxmin.Y, 0);
   BBoxmax.X = MIN(BBoxmax.X, Buffer->w - 1);
   BBoxmax.Y = MIN(BBoxmax.Y, Buffer->h - 1);

   vec3 P= {}; 
    for (P.X=BBoxmin.X; P.X<=BBoxmax.X; P.X++) { 
        for (P.Y=BBoxmin.Y; P.Y<=BBoxmax.Y; P.Y++) { 
            vec3 BarycentricPos  = GetBarycentric(Points[0],Points[1],Points[2], P);
            if (BarycentricPos.X<0 || BarycentricPos.Y<0 || BarycentricPos.Z<0) continue;
            P.Z = 0;
            for (int i=0; i<3; i++){
                P.Z += Points[i].Elements[2]*BarycentricPos.Elements[i];
            }
            //Interpolating UV to get color
                vec2 UVP = {};
                UVP.X = BarycentricPos.X * UV[0].X + BarycentricPos.Y * UV[1].X + BarycentricPos.Z * UV[2].X;
                UVP.Y = BarycentricPos.X * UV[0].Y + BarycentricPos.Y * UV[1].Y + BarycentricPos.Z * UV[2].Y;
            //Interpolating Intensity to get light
                float iP = BarycentricPos.X * Intensity[0] + BarycentricPos.Y * Intensity[1] + BarycentricPos.Z * Intensity[2];
            if(Zbuffer[int(P.X+P.Y*Buffer->w)]<P.Z){
                Zbuffer[int(P.X+P.Y*Buffer->w)] = P.Z;
                Uint8 *Pix = (Uint8 *) Texture->pixels + (int)((UVP.Y)*Texture->h) * Texture->pitch +
                    ((int)((1-UVP.X)*Texture->w) )* 4;
                // Write to Pixel in buffer
                Uint32 Pixel = *(Uint32 *)Pix;
                float r = (float)((Pixel & 0x00FF0000) >> Rshift) / 255;
                float g = (float)((Pixel & 0x0000FF00) >> Gshift) / 255;
                float b = (float)((Pixel & 0x000000FF) >> Bshift) / 255;
                float a = (float)((Pixel & 0xFF000000) >> Ashift) / 255;
                DrawPixel(Buffer,P.X, P.Y, r*iP,g*iP,b*iP);
            }
        } 
    }         
}