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/* Must match eGPLayerBlendModes */
#define MODE_REGULAR 0
#define MODE_HARDLIGHT 1
#define MODE_ADD 2
#define MODE_SUB 3
#define MODE_MULTIPLY 4
#define MODE_DIVIDE 5
#define MODE_HARDLIGHT_SECOND_PASS 999
void blend_mode_output(
int blend_mode, vec4 color, float opacity, out vec4 frag_color, out vec4 frag_revealage)
{
switch (blend_mode) {
case MODE_REGULAR:
/* Reminder: Blending func is premult alpha blend `(dst.rgba * (1 - src.a) + src.rgb)`. */
color *= opacity;
frag_color = color;
frag_revealage = vec4(0.0, 0.0, 0.0, color.a);
break;
case MODE_MULTIPLY:
/* Reminder: Blending func is multiply blend `(dst.rgba * src.rgba)`. */
color.a *= opacity;
frag_revealage = frag_color = (1.0 - color.a) + color.a * color;
break;
case MODE_DIVIDE:
/* Reminder: Blending func is multiply blend `(dst.rgba * src.rgba)`. */
color.a *= opacity;
frag_revealage = frag_color = clamp(1.0 / max(vec4(1e-6), 1.0 - color * color.a), 0.0, 1e18);
break;
case MODE_HARDLIGHT: {
/* Reminder: Blending func is multiply blend `(dst.rgba * src.rgba)`. */
/**
* We need to separate the overlay equation into 2 term (one mul and one add).
* This is the standard overlay equation (per channel):
* `rtn = (src < 0.5) ? (2.0 * src * dst) : (1.0 - 2.0 * (1.0 - src) * (1.0 - dst));`
* We rewrite the second branch like this:
* `rtn = 1 - 2 * (1 - src) * (1 - dst);`
* `rtn = 1 - 2 (1 - dst + src * dst - src);`
* `rtn = 1 - 2 (1 - dst * (1 - src) - src);`
* `rtn = 1 - 2 + dst * (2 - 2 * src) + 2 * src;`
* `rtn = (- 1 + 2 * src) + dst * (2 - 2 * src);`
*/
color = mix(vec4(0.5), color, color.a * opacity);
vec4 s = step(-0.5, -color);
frag_revealage = frag_color = 2.0 * s + 2.0 * color * (1.0 - s * 2.0);
frag_revealage = max(vec4(0.0), frag_revealage);
break;
}
case MODE_HARDLIGHT_SECOND_PASS:
/* Reminder: Blending func is additive blend (dst.rgba + src.rgba). */
color = mix(vec4(0.5), color, color.a * opacity);
frag_revealage = frag_color = (-1.0 + 2.0 * color) * step(-0.5, -color);
frag_revealage = max(vec4(0.0), frag_revealage);
break;
case MODE_SUB:
case MODE_ADD:
/* Reminder: Blending func is additive / subtractive blend `(dst.rgba +/- src.rgba)`. */
frag_color = color * color.a * opacity;
frag_revealage = vec4(0.0);
break;
}
}
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