1 // fast painter for composition modes which can be implemented with blendfuncs

     2 

     3 uniform sampler2D mask_texture;

     4 uniform vec2 inv_mask_size;

     5 uniform vec2 mask_offset;

     6 uniform vec4 mask_channel;

     7 

     8 float mask()

     9 {

    10     return dot(mask_channel, texture2D(mask_texture, (gl_FragCoord.xy + mask_offset) * inv_mask_size));

    11 }

    12 

    13 void main()

    14 {

    15     // combine clip and coverage channels

    16     float mask_alpha = mask();

    17 

    18     gl_FragColor = brush() * mask_alpha;

    19 }