SuperTuxKart 1.5 upstream source (from official release tarball)

data/shaders/sp_ghost.frag

@@ -0,0 +1,34 @@
+uniform float custom_alpha;
+
+in float hue_change;
+
+in vec2 uv;
+in vec4 color;
+out vec4 o_diffuse_color;
+
+#stk_include "utils/rgb_conversion.frag"
+#stk_include "utils/sp_texture_sampling.frag"
+
+void main()
+{
+    vec4 col = sampleTextureLayer0(uv);
+    if (hue_change > 0.0)
+    {
+        float mask = col.a;
+        vec3 old_hsv = rgbToHsv(col.rgb);
+        float mask_step = step(mask, 0.5);
+#if !defined(Advanced_Lighting_Enabled)
+        // For similar color
+        float saturation = mask * 1.825; // 2.5 * 0.5 ^ (1. / 2.2)
+#else
+        float saturation = mask * 2.5;
+#endif
+        vec2 new_xy = mix(vec2(old_hsv.x, old_hsv.y), vec2(hue_change,
+            max(old_hsv.y, saturation)), vec2(mask_step, mask_step));
+        vec3 new_color = hsvToRgb(vec3(new_xy.x, new_xy.y, old_hsv.z));
+        col = vec4(new_color.r, new_color.g, new_color.b, 1.0);
+    }
+
+    vec3 final_color = col.xyz * color.xyz;
+    o_diffuse_color = vec4((final_color * custom_alpha), custom_alpha);
+}