Fix T62259: RGB Curves behave differently in Cycles and Eevee

This was due to curve being not extrapolated correctly. Also curvemap range
was not taken into account.

1 files changed, 42 insertions, 9 deletions

diff --git a/source/blender/gpu/shaders/gpu_shader_material.glsl b/source/blender/gpu/shaders/gpu_shader_material.glsl
index a7231bda263..422487d075d 100644
--- a/source/blender/gpu/shaders/gpu_shader_material.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_material.glsl
@@ -479,16 +479,49 @@ void curves_vec(float fac, vec3 vec, sampler1DArray curvemap, float layer, out v
 	outvec = mix(vec, outvec, fac);
 }
 
-void curves_rgb(float fac, vec4 col, sampler1DArray curvemap, float layer, out vec4 outcol)
-{
-	vec4 co = vec4(col.rgb, layer);
-	co.x = texture(curvemap, co.xw).a;
-	co.y = texture(curvemap, co.yw).a;
-	co.z = texture(curvemap, co.zw).a;
-	outcol.r = texture(curvemap, co.xw).r;
-	outcol.g = texture(curvemap, co.yw).g;
-	outcol.b = texture(curvemap, co.zw).b;
+/* ext is vec4(in_x, in_dy, out_x, out_dy). */
+float curve_extrapolate(float x, float y, vec4 ext)
+{
+	if (x < 0.0) {
+		return y + x * ext.y;
+	}
+	else if (x > 1.0) {
+		return y + (x - 1.0) * ext.w;
+	}
+	else {
+		return y;
+	}
+}
+
+#define RANGE_RESCALE(x, min, range) ((x - min) * range)
+
+void curves_rgb(
+        float fac, vec4 col, sampler1DArray curvemap, float layer,
+        vec4 range, vec4 ext_r, vec4 ext_g, vec4 ext_b, vec4 ext_a,
+        out vec4 outcol)
+{
+	vec4 co = vec4(RANGE_RESCALE(col.rgb, ext_a.x, range.a), layer);
+	vec3 samp;
+	samp.r = texture(curvemap, co.xw).a;
+	samp.g = texture(curvemap, co.yw).a;
+	samp.b = texture(curvemap, co.zw).a;
+
+	samp.r = curve_extrapolate(co.x, samp.r, ext_a);
+	samp.g = curve_extrapolate(co.y, samp.g, ext_a);
+	samp.b = curve_extrapolate(co.z, samp.b, ext_a);
+
+	vec3 rgb_min = vec3(ext_r.x, ext_g.x, ext_b.x);
+	co.xyz = RANGE_RESCALE(samp.rgb, rgb_min, range.rgb);
+
+	samp.r = texture(curvemap, co.xw).r;
+	samp.g = texture(curvemap, co.yw).g;
+	samp.b = texture(curvemap, co.zw).b;
+
+	outcol.r = curve_extrapolate(co.x, samp.r, ext_r);
+	outcol.g = curve_extrapolate(co.y, samp.g, ext_g);
+	outcol.b = curve_extrapolate(co.z, samp.b, ext_b);
 	outcol.a = col.a;
+
 	outcol = mix(col, outcol, fac);
 }