Fix T70644 EEVEE: Bump issue with geometry node normal coordinate

Was caused by non-normalized coordinates (normals). Note this is not 100%
correct as the dFdx functions can be the same for packs of 4 pixels and the
derivated value can only be correct for one pixels.

This is because smoothed normals are a non-linear function (because of the
normalization).

The correct fix would be to do the dFdx offset BEFORE any normalization.

2 files changed, 16 insertions, 0 deletions

diff --git a/source/blender/nodes/shader/nodes/node_shader_geometry.c b/source/blender/nodes/shader/nodes/node_shader_geometry.c
index 54a5411114a..3798cfbbfac 100644
--- a/source/blender/nodes/shader/nodes/node_shader_geometry.c
+++ b/source/blender/nodes/shader/nodes/node_shader_geometry.c
@@ -62,6 +62,14 @@ static int node_shader_gpu_geometry(GPUMaterial *mat,
   /* for each output */
   for (int i = 0; sh_node_geometry_out[i].type != -1; i++) {
     node_shader_gpu_bump_tex_coord(mat, node, &out[i].link);
+    /* Normalize some vectors after dFdx/dFdy offsets.
+     * This is the case for interpolated, non linear functions.
+     * The resulting vector can still be a bit wrong but not as much.
+     * (see T70644) */
+    if (node->branch_tag != 0 && ELEM(i, 1, 2, 4)) {
+      GPU_link(
+          mat, "vector_math_normalize", out[i].link, out[i].link, out[i].link, &out[i].link, NULL);
+    }
   }
 
   return success;
diff --git a/source/blender/nodes/shader/nodes/node_shader_tex_coord.c b/source/blender/nodes/shader/nodes/node_shader_tex_coord.c
index 068458b7e1f..8bb17acc4d3 100644
--- a/source/blender/nodes/shader/nodes/node_shader_tex_coord.c
+++ b/source/blender/nodes/shader/nodes/node_shader_tex_coord.c
@@ -63,6 +63,14 @@ static int node_shader_gpu_tex_coord(GPUMaterial *mat,
   /* for each output. */
   for (int i = 0; sh_node_tex_coord_out[i].type != -1; i++) {
     node_shader_gpu_bump_tex_coord(mat, node, &out[i].link);
+    /* Normalize some vectors after dFdx/dFdy offsets.
+     * This is the case for interpolated, non linear functions.
+     * The resulting vector can still be a bit wrong but not as much.
+     * (see T70644) */
+    if (node->branch_tag != 0 && ELEM(i, 1, 6)) {
+      GPU_link(
+          mat, "vector_math_normalize", out[i].link, out[i].link, out[i].link, &out[i].link, NULL);
+    }
   }
 
   return 1;