1 uniform sampler2D dst_texture;

     2 uniform sampler2D mask_texture;

     3 uniform vec2 inv_mask_size;

     4 uniform vec2 inv_dst_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     vec4 dst = texture2D(dst_texture, gl_FragCoord.xy * inv_dst_size);

    16 

    17     // combine clip and coverage channels

    18     float mask_alpha = mask();

    19 

    20     gl_FragColor = mix(dst, composite(brush(), dst), mask_alpha);

    21 }