1 files changed, 80 insertions, 0 deletions
diff --git a/source/blender/draw/intern/shaders/common_subdiv_vbo_edituv_strech_angle_comp.glsl b/source/blender/draw/intern/shaders/common_subdiv_vbo_edituv_strech_angle_comp.glsl
new file mode 100644
index 00000000000..ea73b9482d3
--- /dev/null
+++ b/source/blender/draw/intern/shaders/common_subdiv_vbo_edituv_strech_angle_comp.glsl
@@ -0,0 +1,80 @@
+
+/* To be compile with common_subdiv_lib.glsl */
+
+layout(std430, binding = 0) readonly buffer inputVerts
+{
+  PosNorLoop pos_nor[];
+};
+
+layout(std430, binding = 1) readonly buffer inputUVs
+{
+  vec2 uvs[];
+};
+
+/* Mirror of #UVStretchAngle in the C++ code, but using floats until proper data compression
+ * is implemented for all subdivision data. */
+struct UVStretchAngle {
+  float angle;
+  float uv_angle0;
+  float uv_angle1;
+};
+
+layout(std430, binding = 2) writeonly buffer outputStretchAngles
+{
+  UVStretchAngle uv_stretches[];
+};
+
+#define M_PI 3.1415926535897932
+#define M_1_PI 0.31830988618379067154
+
+/* Adapted from BLI_math_vector.h */
+float angle_normalized_v3v3(vec3 v1, vec3 v2)
+{
+  /* this is the same as acos(dot_v3v3(v1, v2)), but more accurate */
+  bool q = (dot(v1, v2) >= 0.0);
+  vec3 v = (q) ? (v1 - v2) : (v1 + v2);
+  float a = 2.0 * asin(length(v) / 2.0);
+  return (q) ? a : M_PI - a;
+}
+
+void main()
+{
+  /* We execute for each quad. */
+  uint quad_index = get_global_invocation_index();
+  if (quad_index >= total_dispatch_size) {
+    return;
+  }
+
+  uint start_loop_index = quad_index * 4;
+
+  for (uint i = 0; i < 4; i++) {
+    uint cur_loop_index = start_loop_index + i;
+    uint next_loop_index = start_loop_index + (i + 1) % 4;
+    uint prev_loop_index = start_loop_index + (i + 3) % 4;
+
+    /* Compute 2d edge vectors from UVs. */
+    vec2 cur_uv = uvs[src_offset + cur_loop_index];
+    vec2 next_uv = uvs[src_offset + next_loop_index];
+    vec2 prev_uv = uvs[src_offset + prev_loop_index];
+
+    vec2 norm_uv_edge0 = normalize(prev_uv - cur_uv);
+    vec2 norm_uv_edge1 = normalize(cur_uv - next_uv);
+
+    /* Compute 3d edge vectors from positions. */
+    vec3 cur_pos = get_vertex_pos(pos_nor[cur_loop_index]);
+    vec3 next_pos = get_vertex_pos(pos_nor[next_loop_index]);
+    vec3 prev_pos = get_vertex_pos(pos_nor[prev_loop_index]);
+
+    vec3 norm_pos_edge0 = normalize(prev_pos - cur_pos);
+    vec3 norm_pos_edge1 = normalize(cur_pos - next_pos);
+
+    /* Compute stretches, this logic is adapted from #edituv_get_edituv_stretch_angle.
+     * Keep in sync! */
+    UVStretchAngle stretch;
+    stretch.uv_angle0 = atan(norm_uv_edge0.y, norm_uv_edge0.x) * M_1_PI;
+    stretch.uv_angle1 = atan(norm_uv_edge1.y, norm_uv_edge1.x) * M_1_PI;
+    stretch.angle = angle_normalized_v3v3(norm_pos_edge0, norm_pos_edge1) * M_1_PI;
+
+    uv_stretches[cur_loop_index] = stretch;
+  }
+}