1 files changed, 16 insertions, 0 deletions
diff --git a/source/blender/gpu/intern/gpu_shader_material.glsl b/source/blender/gpu/intern/gpu_shader_material.glsl
index feb0a84fa87..0aae6d84a01 100644
--- a/source/blender/gpu/intern/gpu_shader_material.glsl
+++ b/source/blender/gpu/intern/gpu_shader_material.glsl
@@ -1226,6 +1226,22 @@ void mtex_bump_tap5( vec3 texco, sampler2D ima, float hScale,
 	dBt = hScale * (Hu - Hd);
 }
 
+void mtex_bump_deriv( vec3 texco, sampler2D ima, float ima_x, float ima_y, float hScale, 
+                     out float dBs, out float dBt ) 
+{
+	float s = 1;		// negate this if flipped texture coordinate
+	vec2 TexDx = dFdx(texco.xy);
+	vec2 TexDy = dFdy(texco.xy);
+	
+	// this variant using a derivative map is described here
+	// http://mmikkelsen3d.blogspot.com/2011/07/derivative-maps.html
+	vec2 dim = vec2(ima_x, ima_y);
+	vec2 dBduv = hScale*dim*(2*texture2D(ima, texco.xy).xy-1);
+	
+	dBs = dBduv.x*TexDx.x + s*dBduv.y*TexDx.y;
+	dBt = dBduv.x*TexDy.x + s*dBduv.y*TexDy.y;
+}
+
 void mtex_bump_apply( float fDet, float dBs, float dBt, vec3 vR1, vec3 vR2, vec3 vNacc_in,
 					  out vec3 vNacc_out, out vec3 perturbed_norm ) 
 {