// this is the top right corner of our sprite quad.
var v:Vector3D = new Vector3D(128, -128, 0, 1);
 
// this is the sprites matrix, translated a bit
var clipSpaceMatrix:Matrix3D = new Matrix3D();
clipSpaceMatrix.appendTranslation(100, 0, 0);
// this is the masks matrix, it's in the same position as the sprite
var maskClipSpaceMatrix:Matrix3D = new Matrix3D();
maskClipSpaceMatrix.appendTranslation(100, 0, 0);
// this is the masks size
var maskBitmap:Rectangle = new Rectangle(0, 0, 256, 256);
 
// invert the matrix, because we want to map back from world space to local mask space
maskClipSpaceMatrix.invert();
 
// transform our vertex from local sprite space to world space
v = clipSpaceMatrix.transformVector(v);
[trace] moved to clipspace: Vector3D(228, -128, 0)
 
// transform world space vertex back to local mask space
// the result is the same vector of course, because the positions of mask and sprite are equal
v = maskClipSpaceMatrix.transformVector(v);
[trace] moved to local mask space: Vector3D(128, -128, 0)
 
// calculate the uv coordinates from the local pixel position
v = new Vector3D((v.x + (maskBitmap.width * 0.5)) / maskBitmap.width,
                 (v.y + (maskBitmap.height * 0.5)) / maskBitmap.height,
                  0.0, 1.0);
 
// the result is what we expect, the top right uv coordinate:
[trace] local mask uv: Vector3D(1, 0, 0)

void evaluateVertex()
{
     interpolatedUV = float4(uvCoord.x + uvOffset.x, uvCoord.y + uvOffset.y, 0.0, 0.0);
 
     float4 worldSpacePos = float4(vertexPos.x, vertexPos.y, 0.0, 1.0) * objectToClipSpaceTransform;
     // maskObjectToClipSpaceTransform is the invertex clipspace matrix of the mask
     float4 localMaskSpacePos = worldSpacePos * maskObjectToClipSpaceTransform;
 
     // halfMaskSize.xy is maskBitmap.width/height * 0.5 passed as a parameter
     // invertedMaskSize.xy = 1.0 / maskBitmap.width/height passed as a parameter, because divisions are not properly working in the current pb3d release
     interpolatedMaskUV = float4((localMaskSpacePos.x + halfMaskSize.x) * invertedMaskSize.x,
                                 (localMaskSpacePos.y + halfMaskSize.y) * invertedMaskSize.y,
                                  0.0, 0.0);
}
 
void evaluateFragment()
{
    float4 texel = sample(textureImage, float2(interpolatedUV.x, interpolatedUV.y), PB3D_2D | PB3D_MIPNEAREST | PB3D_CLAMP);
    float4 texel2 = sample(textureMaskImage, float2(interpolatedMaskUV.x, interpolatedMaskUV.y), PB3D_2D | PB3D_MIPNEAREST | PB3D_CLAMP);
 
    result = float4(texel.r * color.r * texel2.r,
                    texel.g * color.g * texel2.g,
                    texel.b * color.b * texel2.b,
                    texel.a * color.a * texel2.a);
}

/*
vertex shader:
 
vc0-vc3 = clipspace matrix of sprite
vc4-vc7 = inverted clipspace matrix of mask
vc8.xy = half mask width / height
vc8.zw = mask width / height
va0 = vertex
va1 = uv
*/
 
m44 vt0, va0, vc0           // vertex * clipspace
m44 vt1, vt0, vc4           // clipspace to local pos in mask
add vt1.xy, vt1.xy, vc8.xy  // add half masksize to local pos
div vt1.xy, vt1.xy, vc8.zw  // local pos / masksize
mov v0, va1                 // copy uv
mov v1, vt1                 // copy mask uv
mov op, vt0                 // output position
 
/*
fragment shader:
*/
 
mov ft0, v0                                // get interpolated uv coords
tex ft1, ft0, fs0 <2d,clamp,linear,nomip>  // sample texture
mov ft2, v1                                // get interpolated uv coords for mask
tex ft3, ft2, fs1 <2d,clamp,linear,nomip>  // sample mask
mul ft1, ft1, ft3                          // mult mask color with tex color
mov oc, ft1                                // output color