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

4 files changed, 66 insertions, 49 deletions

diff --git a/source/blender/draw/intern/draw_cache_extract.h b/source/blender/draw/intern/draw_cache_extract.h
index 9305dc6eef7..70778ca6014 100644
--- a/source/blender/draw/intern/draw_cache_extract.h
+++ b/source/blender/draw/intern/draw_cache_extract.h
@@ -136,8 +136,8 @@ typedef enum DRWBatchFlag {
   MBC_EDIT_LNOR = (1 << 6),
   MBC_EDIT_FACEDOTS = (1 << 7),
   MBC_EDIT_MESH_ANALYSIS = (1 << 8),
-  MBC_EDITUV_FACES_STRECH_AREA = (1 << 9),
-  MBC_EDITUV_FACES_STRECH_ANGLE = (1 << 10),
+  MBC_EDITUV_FACES_STRETCH_AREA = (1 << 9),
+  MBC_EDITUV_FACES_STRETCH_ANGLE = (1 << 10),
   MBC_EDITUV_FACES = (1 << 11),
   MBC_EDITUV_EDGES = (1 << 12),
   MBC_EDITUV_VERTS = (1 << 13),
@@ -157,7 +157,7 @@ typedef enum DRWBatchFlag {
 } DRWBatchFlag;
 
 #define MBC_EDITUV \
-  (MBC_EDITUV_FACES_STRECH_AREA | MBC_EDITUV_FACES_STRECH_ANGLE | MBC_EDITUV_FACES | \
+  (MBC_EDITUV_FACES_STRETCH_AREA | MBC_EDITUV_FACES_STRETCH_ANGLE | MBC_EDITUV_FACES | \
    MBC_EDITUV_EDGES | MBC_EDITUV_VERTS | MBC_EDITUV_FACEDOTS | MBC_WIRE_LOOPS_UVS)
 
 #define FOREACH_MESH_BUFFER_CACHE(batch_cache, mbc) \
@@ -183,8 +183,8 @@ typedef struct MeshBatchCache {
     GPUBatch *edit_fdots;
     GPUBatch *edit_mesh_analysis;
     /* Edit UVs */
-    GPUBatch *edituv_faces_strech_area;
-    GPUBatch *edituv_faces_strech_angle;
+    GPUBatch *edituv_faces_stretch_area;
+    GPUBatch *edituv_faces_stretch_angle;
     GPUBatch *edituv_faces;
     GPUBatch *edituv_edges;
     GPUBatch *edituv_verts;
@@ -234,6 +234,12 @@ typedef struct MeshBatchCache {
   /* Valid only if edge_detection is up to date. */
   bool is_manifold;
 
+  /* Total areas for drawing UV Stretching. Contains the summed area in mesh
+   * space (`tot_area`) and the summed area in uv space (`tot_uvarea`).
+   *
+   * Only valid after `DRW_mesh_batch_cache_create_requested` has been called. */
+  float tot_area, tot_uv_area;
+
   bool no_loose_wire;
 } MeshBatchCache;
 
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. */
diff --git a/source/blender/draw/intern/draw_cache_impl.h b/source/blender/draw/intern/draw_cache_impl.h
index 3e33346c7d8..970b6053cf9 100644
--- a/source/blender/draw/intern/draw_cache_impl.h
+++ b/source/blender/draw/intern/draw_cache_impl.h
@@ -150,8 +150,10 @@ struct GPUBatch *DRW_mesh_batch_cache_get_verts_with_select_id(struct Mesh *me);
 /* Object mode Wireframe overlays */
 struct GPUBatch *DRW_mesh_batch_cache_get_wireframes_face(struct Mesh *me);
 /* edit-mesh UV editor */
-struct GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_strech_area(struct Mesh *me);
-struct GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_strech_angle(struct Mesh *me);
+struct GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_stretch_area(struct Mesh *me,
+                                                                    float *tot_area,
+                                                                    float *tot_uv_area);
+struct GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_stretch_angle(struct Mesh *me);
 struct GPUBatch *DRW_mesh_batch_cache_get_edituv_faces(struct Mesh *me);
 struct GPUBatch *DRW_mesh_batch_cache_get_edituv_edges(struct Mesh *me);
 struct GPUBatch *DRW_mesh_batch_cache_get_edituv_verts(struct Mesh *me);
diff --git a/source/blender/draw/intern/draw_cache_impl_mesh.c b/source/blender/draw/intern/draw_cache_impl_mesh.c
index 456e21db6ed..96c677dc184 100644
--- a/source/blender/draw/intern/draw_cache_impl_mesh.c
+++ b/source/blender/draw/intern/draw_cache_impl_mesh.c
@@ -502,14 +502,17 @@ static void mesh_batch_cache_discard_uvedit(MeshBatchCache *cache)
     GPU_INDEXBUF_DISCARD_SAFE(mbufcache->ibo.edituv_points);
     GPU_INDEXBUF_DISCARD_SAFE(mbufcache->ibo.edituv_fdots);
   }
-  GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_strech_area);
-  GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_strech_angle);
+  GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_stretch_area);
+  GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_stretch_angle);
   GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces);
   GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_edges);
   GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_verts);
   GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_fdots);
   GPU_BATCH_DISCARD_SAFE(cache->batch.wire_loops_uvs);
 
+  cache->tot_area = 0.0f;
+  cache->tot_uv_area = 0.0f;
+
   cache->batch_ready &= ~MBC_EDITUV;
 }
 
@@ -577,8 +580,8 @@ void DRW_mesh_batch_cache_dirty_tag(Mesh *me, int mode)
         GPU_VERTBUF_DISCARD_SAFE(mbufcache->vbo.edituv_data);
         GPU_VERTBUF_DISCARD_SAFE(mbufcache->vbo.fdots_edituv_data);
       }
-      GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_strech_area);
-      GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_strech_angle);
+      GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_stretch_area);
+      GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces_stretch_angle);
       GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_faces);
       GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_edges);
       GPU_BATCH_DISCARD_SAFE(cache->batch.edituv_verts);
@@ -874,20 +877,34 @@ GPUBatch *DRW_mesh_batch_cache_get_verts_with_select_id(Mesh *me)
 /** \name UV Image editor API
  * \{ */
 
-GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_strech_area(Mesh *me)
+/* Creates the GPUBatch for drawing the UV Stretching Area Overlay.
+ * Optional retrieves the total area or total uv area of the mesh.
+ *
+ * The `cache->tot_area` and cache->tot_uv_area` update are calculation are
+ * only valid after calling `DRW_mesh_batch_cache_create_requested`. */
+GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_stretch_area(Mesh *me,
+                                                             float *tot_area,
+                                                             float *tot_uv_area)
 {
   MeshBatchCache *cache = mesh_batch_cache_get(me);
   texpaint_request_active_uv(cache, me);
-  mesh_batch_cache_add_request(cache, MBC_EDITUV_FACES_STRECH_AREA);
-  return DRW_batch_request(&cache->batch.edituv_faces_strech_area);
+  mesh_batch_cache_add_request(cache, MBC_EDITUV_FACES_STRETCH_AREA);
+
+  if (tot_area != NULL) {
+    *tot_area = cache->tot_area;
+  }
+  if (tot_uv_area != NULL) {
+    *tot_uv_area = cache->tot_uv_area;
+  }
+  return DRW_batch_request(&cache->batch.edituv_faces_stretch_area);
 }
 
-GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_strech_angle(Mesh *me)
+GPUBatch *DRW_mesh_batch_cache_get_edituv_faces_stretch_angle(Mesh *me)
 {
   MeshBatchCache *cache = mesh_batch_cache_get(me);
   texpaint_request_active_uv(cache, me);
-  mesh_batch_cache_add_request(cache, MBC_EDITUV_FACES_STRECH_ANGLE);
-  return DRW_batch_request(&cache->batch.edituv_faces_strech_angle);
+  mesh_batch_cache_add_request(cache, MBC_EDITUV_FACES_STRETCH_ANGLE);
+  return DRW_batch_request(&cache->batch.edituv_faces_stretch_angle);
 }
 
 GPUBatch *DRW_mesh_batch_cache_get_edituv_faces(Mesh *me)
@@ -1001,8 +1018,8 @@ void DRW_mesh_batch_cache_create_requested(
   }
 
   if (batch_requested &
-      (MBC_SURFACE | MBC_SURF_PER_MAT | MBC_WIRE_LOOPS_UVS | MBC_EDITUV_FACES_STRECH_AREA |
-       MBC_EDITUV_FACES_STRECH_ANGLE | MBC_EDITUV_FACES | MBC_EDITUV_EDGES | MBC_EDITUV_VERTS)) {
+      (MBC_SURFACE | MBC_SURF_PER_MAT | MBC_WIRE_LOOPS_UVS | MBC_EDITUV_FACES_STRETCH_AREA |
+       MBC_EDITUV_FACES_STRETCH_ANGLE | MBC_EDITUV_FACES | MBC_EDITUV_EDGES | MBC_EDITUV_VERTS)) {
     /* Modifiers will only generate an orco layer if the mesh is deformed. */
     if (cache->cd_needed.orco != 0) {
       if (CustomData_get_layer(&me->vdata, CD_ORCO) == NULL) {
@@ -1078,8 +1095,8 @@ void DRW_mesh_batch_cache_create_requested(
         /* We only clear the batches as they may already have been
          * referenced. */
         GPU_BATCH_CLEAR_SAFE(cache->batch.wire_loops_uvs);
-        GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_faces_strech_area);
-        GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_faces_strech_angle);
+        GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_faces_stretch_area);
+        GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_faces_stretch_angle);
         GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_faces);
         GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_edges);
         GPU_BATCH_CLEAR_SAFE(cache->batch.edituv_verts);
@@ -1261,17 +1278,17 @@ void DRW_mesh_batch_cache_create_requested(
     DRW_vbo_request(cache->batch.edituv_faces, &mbufcache->vbo.uv);
     DRW_vbo_request(cache->batch.edituv_faces, &mbufcache->vbo.edituv_data);
   }
-  if (DRW_batch_requested(cache->batch.edituv_faces_strech_area, GPU_PRIM_TRIS)) {
-    DRW_ibo_request(cache->batch.edituv_faces_strech_area, &mbufcache->ibo.edituv_tris);
-    DRW_vbo_request(cache->batch.edituv_faces_strech_area, &mbufcache->vbo.uv);
-    DRW_vbo_request(cache->batch.edituv_faces_strech_area, &mbufcache->vbo.edituv_data);
-    DRW_vbo_request(cache->batch.edituv_faces_strech_area, &mbufcache->vbo.stretch_area);
-  }
-  if (DRW_batch_requested(cache->batch.edituv_faces_strech_angle, GPU_PRIM_TRIS)) {
-    DRW_ibo_request(cache->batch.edituv_faces_strech_angle, &mbufcache->ibo.edituv_tris);
-    DRW_vbo_request(cache->batch.edituv_faces_strech_angle, &mbufcache->vbo.uv);
-    DRW_vbo_request(cache->batch.edituv_faces_strech_angle, &mbufcache->vbo.edituv_data);
-    DRW_vbo_request(cache->batch.edituv_faces_strech_angle, &mbufcache->vbo.stretch_angle);
+  if (DRW_batch_requested(cache->batch.edituv_faces_stretch_area, GPU_PRIM_TRIS)) {
+    DRW_ibo_request(cache->batch.edituv_faces_stretch_area, &mbufcache->ibo.edituv_tris);
+    DRW_vbo_request(cache->batch.edituv_faces_stretch_area, &mbufcache->vbo.uv);
+    DRW_vbo_request(cache->batch.edituv_faces_stretch_area, &mbufcache->vbo.edituv_data);
+    DRW_vbo_request(cache->batch.edituv_faces_stretch_area, &mbufcache->vbo.stretch_area);
+  }
+  if (DRW_batch_requested(cache->batch.edituv_faces_stretch_angle, GPU_PRIM_TRIS)) {
+    DRW_ibo_request(cache->batch.edituv_faces_stretch_angle, &mbufcache->ibo.edituv_tris);
+    DRW_vbo_request(cache->batch.edituv_faces_stretch_angle, &mbufcache->vbo.uv);
+    DRW_vbo_request(cache->batch.edituv_faces_stretch_angle, &mbufcache->vbo.edituv_data);
+    DRW_vbo_request(cache->batch.edituv_faces_stretch_angle, &mbufcache->vbo.stretch_angle);
   }
   if (DRW_batch_requested(cache->batch.edituv_edges, GPU_PRIM_LINES)) {
     DRW_ibo_request(cache->batch.edituv_edges, &mbufcache->ibo.edituv_lines);