test.frag

#ifdef GL_ES
precision mediump float;
#else
#define mediump
#endif

uniform sampler2D sheet; // spritesheet texture
uniform vec2 filterResolution; // size of filter
uniform vec2 sheetResolution; // native ACTUAL size of spritesheet
uniform vec2 maskXY; // xy of mask sprite

uniform sampler2D tex0;

varying vec2 tcoord;
varying vec4 color;

void main() {
	
    vec4 texColor, maskColor;
    
    texColor = texture2D(tex0, tcoord);
    maskColor = texture2D(sheet, (tcoord * filterResolution + maskXY) / sheetResolution.x);
    
    if (maskColor.a < 0.1) discard;
    
    gl_FragColor = color * texColor;
}