Fix T63755: Area Stretching Overlay

Support for UV Stretching overlay during multi object editing. The
VBO now holds the ratios per fase. In the shader these ratios will
be compared against the global ratios. The global rations are created
from all selected objects.

The current implementation does not fit well with the draw module. The
plan is to move the drawing of other spaces towards the draw manager what
leads to a better fit. Currently the details on this solution is unclear
but this requirement will become an attentionpoint in the future design.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D5665

1 files changed, 9 insertions, 17 deletions

diff --git a/source/blender/draw/intern/draw_cache_extract_mesh.c b/source/blender/draw/intern/draw_cache_extract_mesh.c
index d952965de35..8bca2ad2c45 100644
--- a/source/blender/draw/intern/draw_cache_extract_mesh.c
+++ b/source/blender/draw/intern/draw_cache_extract_mesh.c
@@ -2676,7 +2676,7 @@ static void *extract_stretch_area_init(const MeshRenderData *mr, void *buf)
 {
   static GPUVertFormat format = {0};
   if (format.attr_len == 0) {
-    GPU_vertformat_attr_add(&format, "stretch", GPU_COMP_U16, 1, GPU_FETCH_INT_TO_FLOAT_UNIT);
+    GPU_vertformat_attr_add(&format, "ratio", GPU_COMP_U16, 1, GPU_FETCH_INT_TO_FLOAT_UNIT);
   }
 
   GPUVertBuf *vbo = buf;
@@ -2703,7 +2703,7 @@ BLI_INLINE float area_ratio_to_stretch(float ratio, float tot_ratio, float inv_t
 
 static void mesh_stretch_area_finish(const MeshRenderData *mr, void *buf, void *UNUSED(data))
 {
-  float totarea = 0, totuvarea = 0;
+  float tot_area = 0.0f, tot_uv_area = 0.0f;
   float *area_ratio = MEM_mallocN(sizeof(float) * mr->poly_len, __func__);
 
   if (mr->extract_type == MR_EXTRACT_BMESH) {
@@ -2716,8 +2716,8 @@ static void mesh_stretch_area_finish(const MeshRenderData *mr, void *buf, void *
     BM_ITER_MESH_INDEX (efa, &f_iter, mr->bm, BM_FACES_OF_MESH, f) {
       float area = BM_face_calc_area(efa);
       float uvarea = BM_face_calc_area_uv(efa, uv_ofs);
-      totarea += area;
-      totuvarea += uvarea;
+      tot_area += area;
+      tot_uv_area += uvarea;
       area_ratio[f] = area_ratio_get(area, uvarea);
     }
   }
@@ -2727,8 +2727,8 @@ static void mesh_stretch_area_finish(const MeshRenderData *mr, void *buf, void *
     for (int p = 0; p < mr->poly_len; p++, mpoly++) {
       float area = BKE_mesh_calc_poly_area(mpoly, &mr->mloop[mpoly->loopstart], mr->mvert);
       float uvarea = BKE_mesh_calc_poly_uv_area(mpoly, uv_data);
-      totarea += area;
-      totuvarea += uvarea;
+      tot_area += area;
+      tot_uv_area += uvarea;
       area_ratio[p] = area_ratio_get(area, uvarea);
     }
   }
@@ -2737,21 +2737,13 @@ static void mesh_stretch_area_finish(const MeshRenderData *mr, void *buf, void *
     BLI_assert(0);
   }
 
-  float tot_ratio, inv_tot_ratio;
-  if (totarea < FLT_EPSILON || totuvarea < FLT_EPSILON) {
-    tot_ratio = 0.0f;
-    inv_tot_ratio = 0.0f;
-  }
-  else {
-    tot_ratio = totarea / totuvarea;
-    inv_tot_ratio = totuvarea / totarea;
-  }
+  mr->cache->tot_area = tot_area;
+  mr->cache->tot_uv_area = tot_uv_area;
 
   /* Convert in place to avoid an extra allocation */
   uint16_t *poly_stretch = (uint16_t *)area_ratio;
   for (int p = 0; p < mr->poly_len; p++) {
-    float stretch = area_ratio_to_stretch(area_ratio[p], tot_ratio, inv_tot_ratio);
-    poly_stretch[p] = (1.0f - stretch) * 65534.0f;
+    poly_stretch[p] = area_ratio[p] * 65534.0f;
   }
 
   /* Copy face data for each loop. */