Eevee: Use manual derivatives for better quality bump.

We basically duplicate the height map branch plugged into the bump node,
and tag each node in each branch as dx/dy/ref using `branch_tag`.

Then we add a one pixel offset on the texture coordinates if the node is
tagged as dx or dy.

The dx/dy branches are plugged into (new) hidden sockets on the bump node.

This match cycles bump better but have a performance impact. Also, complex
nodetrees can now become instruction limited and not compile anymore.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D5531

1 files changed, 21 insertions, 4 deletions

diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_bump.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_bump.glsl
index 1137e5acdc6..fabc070b0bc 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_bump.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_bump.glsl
@@ -1,5 +1,22 @@
-void node_bump(
-    float strength, float dist, float height, vec3 N, vec3 surf_pos, float invert, out vec3 result)
+void dfdx_v3(vec3 v, out vec3 dy)
+{
+  dy = v + abs(dFdx(v));
+}
+
+void dfdy_v3(vec3 v, out vec3 dy)
+{
+  dy = v + abs(dFdy(v));
+}
+
+void node_bump(float strength,
+               float dist,
+               float height,
+               float height_dx,
+               float height_dy,
+               vec3 N,
+               vec3 surf_pos,
+               float invert,
+               out vec3 result)
 {
   N = mat3(ViewMatrix) * normalize(N);
   dist *= gl_FrontFacing ? invert : -invert;
@@ -14,8 +31,8 @@ void node_bump(
   /* Compute surface gradient and determinant. */
   float det = dot(dPdx, Rx);
 
-  float dHdx = dFdx(height);
-  float dHdy = dFdy(height);
+  float dHdx = height_dx - height;
+  float dHdy = height_dy - height;
   vec3 surfgrad = dHdx * Rx + dHdy * Ry;
 
   strength = max(strength, 0.0);