[Bf-blender-cvs] [3c2d405cc57] greasepencil-object: GPencil: Scale strokes to Potrace lib units

[Antonio Vazquez]

Commit: 3c2d405cc5751f18fc8024929f8c2ce537f06ac5
Author: Antonio Vazquez
Date:   Thu Aug 20 16:37:07 2020 +0200
Branches: greasepencil-object
https://developer.blender.org/rB3c2d405cc5751f18fc8024929f8c2ce537f06ac5

GPencil: Scale strokes to Potrace lib units

After doing a lot of testing, it looks the library is using a factor base on the VGA resolution and aspect ratio.

The formula was obtained experimenting and gets a very good result, but it could be a totally different approach if we find what logic is used by Potrace.

===================================================================

M	source/blender/editors/gpencil/gpencil_trace_ops.c

===================================================================

diff --git a/source/blender/editors/gpencil/gpencil_trace_ops.c b/source/blender/editors/gpencil/gpencil_trace_ops.c
index 4cac41bc4e1..8f6123d33b8 100644
--- a/source/blender/editors/gpencil/gpencil_trace_ops.c
+++ b/source/blender/editors/gpencil/gpencil_trace_ops.c
@@ -125,8 +125,10 @@ static bool gpencil_trace_image(
   offset[1] = ibuf->y / 2;
 
   /* Scale correction for Potrace. */
-  const float scale_potrace = scale * (640.0f / (float)ibuf->x) *
-                              ((float)ibuf->x / (float)ibuf->y);
+  float scale_potrace = scale * (640.0f / (float)ibuf->x) * ((float)ibuf->x / (float)ibuf->y);
+  if (ibuf->x > ibuf->y) {
+    scale_potrace *= (float)ibuf->y / (float)ibuf->x;
+  }
 
   ED_gpencil_trace_data_to_strokes(
       bmain, st, ob, gpf, offset, scale_potrace, sample, resolution, thickness);