From b83a1b62c7db4e11c96b65cb68b2a88eeab7fcbc Mon Sep 17 00:00:00 2001
From: Antonioya <blendergit@gmail.com>
Date: Tue, 23 Jul 2019 22:29:42 +0200
Subject: [PATCH] Fix T66233: Grease Pencil Swirl Effect not working at origin

If the control object is in the origin the radius is wrongly calculated because the result is 0.

Now, this value is clamped to avoid this situation
---
 .../engines/gpencil/shaders/fx/gpencil_fx_swirl_frag.glsl   | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/source/blender/draw/engines/gpencil/shaders/fx/gpencil_fx_swirl_frag.glsl b/source/blender/draw/engines/gpencil/shaders/fx/gpencil_fx_swirl_frag.glsl
index b226d4f93bc..01d4fe40195 100644
--- a/source/blender/draw/engines/gpencil/shaders/fx/gpencil_fx_swirl_frag.glsl
+++ b/source/blender/draw/engines/gpencil/shaders/fx/gpencil_fx_swirl_frag.glsl
@@ -42,7 +42,11 @@ void main()
   vec2 tc = uv - center;
 
   float dist = length(tc);
-  float pxradius = (ProjectionMatrix[3][3] == 0.0) ? (radius / (loc.z * defaultpixsize)) :
+  float locpixsize = abs((loc.z * defaultpixsize));
+  if (locpixsize == 0) {
+    locpixsize = 1;
+  }
+  float pxradius = (ProjectionMatrix[3][3] == 0.0) ? (radius / locpixsize) :
                                                      (radius / defaultpixsize);
   pxradius = max(pxradius, 1);