1
2uniform sampler2D colorBuffer;
3uniform sampler2D depthBuffer;
4
5uniform int bgType;
6uniform vec4 colorOverride;
7
8in vec4 uvcoordsvar;
9
10out vec4 fragColor;
11
12#define BG_SOLID 0
13#define BG_GRADIENT 1
14#define BG_CHECKER 2
15#define BG_RADIAL 3
16#define BG_SOLID_CHECKER 4
17#define SQRT2 1.4142135623730950488
18
19/* 4x4 bayer matrix prepared for 8bit UNORM precision error. */
20#define P(x) (((x + 0.5) * (1.0 / 16.0) - 0.5) * (1.0 / 255.0))
21const vec4 dither_mat4x4[4] = vec4[4](vec4(P(0.0), P(8.0), P(2.0), P(10.0)),
22                                      vec4(P(12.0), P(4.0), P(14.0), P(6.0)),
23                                      vec4(P(3.0), P(11.0), P(1.0), P(9.0)),
24                                      vec4(P(15.0), P(7.0), P(13.0), P(5.0)));
25
26float dither(void)
27{
28  ivec2 co = ivec2(gl_FragCoord.xy) % 4;
29  return dither_mat4x4[co.x][co.y];
30}
31
32void main()
33{
34  /* The blend equation is:
35   * resutl.rgb = SRC.rgb * (1 - DST.a) + DST.rgb * (SRC.a)
36   * result.a = SRC.a * 0 + DST.a * SRC.a
37   * This removes the alpha channel and put the background behind reference images
38   * while masking the reference images by the render alpha.
39   */
40  float alpha = texture(colorBuffer, uvcoordsvar.st).a;
41  float depth = texture(depthBuffer, uvcoordsvar.st).r;
42
43  vec3 bg_col;
44  vec3 col_high;
45  vec3 col_low;
46
47  /* BG_SOLID_CHECKER selects BG_SOLID when no pixel has been drawn otherwise use the BG_CHERKER.
48   */
49  int bg_type = bgType == BG_SOLID_CHECKER ? (depth == 1.0 ? BG_SOLID : BG_CHECKER) : bgType;
50
51  switch (bg_type) {
52    case BG_SOLID:
53      bg_col = colorBackground.rgb;
54      break;
55    case BG_GRADIENT:
56      /* XXX do interpolation in a non-linear space to have a better visual result. */
57      col_high = pow(colorBackground.rgb, vec3(1.0 / 2.2));
58      col_low = pow(colorBackgroundGradient.rgb, vec3(1.0 / 2.2));
59      bg_col = mix(col_low, col_high, uvcoordsvar.t);
60      /* Convert back to linear. */
61      bg_col = pow(bg_col, vec3(2.2));
62      /*  Dither to hide low precision buffer. (Could be improved) */
63      bg_col += dither();
64      break;
65    case BG_RADIAL:
66      /* Do interpolation in a non-linear space to have a better visual result. */
67      col_high = pow(colorBackground.rgb, vec3(1.0 / 2.2));
68      col_low = pow(colorBackgroundGradient.rgb, vec3(1.0 / 2.2));
69
70      vec2 uv_n = uvcoordsvar.xy - 0.5;
71      bg_col = mix(col_high, col_low, length(uv_n) * SQRT2);
72
73      /* Convert back to linear. */
74      bg_col = pow(bg_col, vec3(2.2));
75      /*  Dither to hide low precision buffer. (Could be improved) */
76      bg_col += dither();
77      break;
78    case BG_CHECKER:
79      float size = sizeChecker * sizePixel;
80      ivec2 p = ivec2(floor(gl_FragCoord.xy / size));
81      bool check = mod(p.x, 2) == mod(p.y, 2);
82      bg_col = (check) ? colorCheckerPrimary.rgb : colorCheckerSecondary.rgb;
83      break;
84  }
85
86  bg_col = mix(bg_col, colorOverride.rgb, colorOverride.a);
87
88  /* Mimic alpha under behavior. Result is premultiplied. */
89  fragColor = vec4(bg_col, 1.0) * (1.0 - alpha);
90
91  /* Special case: If the render is not transparent, do not clear alpha values. */
92  if (depth == 1.0 && alpha == 1.0) {
93    fragColor.a = 1.0;
94  }
95}
96