UI: Perf: Improve ui_draw_dropshadow.

Replace the 12 iterations of UI_draw_roundbox_4fv with only one batch.

This mean less overdraw and less drawcalls.

I had to hack the opacity falloff curve manually to get approximatly the
same result as previous technique. I'm sure with a bit more brain power
somebody could find the perfect function.

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/gpu/shaders/gpu_shader_2D_widget_shadow_frag.glsl b/source/blender/gpu/shaders/gpu_shader_2D_widget_shadow_frag.glsl
new file mode 100644
index 00000000000..7587b2fc18a
--- /dev/null
+++ b/source/blender/gpu/shaders/gpu_shader_2D_widget_shadow_frag.glsl
@@ -0,0 +1,13 @@
+
+in float shadowFalloff;
+
+out vec4 fragColor;
+
+uniform float alpha;
+
+void main()
+{
+	fragColor = vec4(0.0);
+	/* Manual curve fit of the falloff curve of previous drawing method. */
+	fragColor.a = alpha * (shadowFalloff * shadowFalloff * 0.722 + shadowFalloff * 0.277);
+}
\ No newline at end of file