SuperTuxKart 1.5 upstream source (from official release tarball)

data/shaders/utils/displace_utils.frag

@@ -0,0 +1,29 @@
+vec2 getDisplaceShift(float horiz, float vert)
+{
+    vec2 offset = vec2(horiz, vert);
+    offset = 2.0 * offset - 1.0;
+
+    vec4 shiftval;
+    shiftval.r = step(offset.x, 0.0) * -offset.x;
+    shiftval.g = step(0.0, offset.x) * offset.x;
+    shiftval.b = step(offset.y, 0.0) * -offset.y;
+    shiftval.a = step(0.0, offset.y) * offset.y;
+
+    vec2 shift;
+    shift.x = -shiftval.x + shiftval.y;
+    shift.y = -shiftval.z + shiftval.w;
+    return shift;
+}
+
+ivec2 getDisplaceUV(vec2 shift, vec4 viewport, sampler2D displace_mask)
+{
+    ivec2 uv = ivec2(gl_FragCoord.xy);
+    shift *= 0.02 * viewport.zw;
+    ivec2 lo = ivec2(viewport.xy);
+    ivec2 hi = ivec2(viewport.xy + viewport.zw);
+    ivec2 suv = clamp(ivec2(gl_FragCoord.xy) + ivec2(shift), lo, hi);
+    vec2 new_mask = texelFetch(displace_mask, suv, 0).xy;
+    if (!(new_mask.x == 0.0 && new_mask.y == 0.0))
+        uv = suv;
+    return uv;
+}