Fix error using GPU selection cache for selection picking

When calling GPU_select_cache_begin, checking the selection mode used
the last used selection mode, not the one about to be used.

Using border select, then picking would not use the selection cache.

This wasn't noticeable by users as failing to use cache just completes
the selection without it (drawing the depth buffer unnecessarily).

1 files changed, 37 insertions, 7 deletions

diff --git a/source/blender/gpu/intern/gpu_select.c b/source/blender/gpu/intern/gpu_select.c
index aadb52fb49c..958aab65b57 100644
--- a/source/blender/gpu/intern/gpu_select.c
+++ b/source/blender/gpu/intern/gpu_select.c
@@ -61,6 +61,15 @@ typedef struct GPUSelectState {
   char algorithm;
   /* allow GPU_select_begin/end without drawing */
   bool use_cache;
+  /**
+   * Signifies that #GPU_select_cache_begin has been called,
+   * future calls to #GPU_select_begin should initialize the cache.
+   *
+   * \note #GPU_select_cache_begin could perform initialization but doesn't as it's inconvenient
+   * for callers making the cache begin/end calls outside lower level selection logic
+   * where the `mode` to pass to #GPU_select_begin yet isn't known.
+   */
+  bool use_cache_needs_init;
 } GPUSelectState;
 
 static GPUSelectState g_select_state = {0};
@@ -90,9 +99,26 @@ void GPU_select_begin(uint *buffer, uint bufsize, const rcti *input, char mode,
     g_select_state.algorithm = ALGO_GL_QUERY;
   }
 
+  /* This function is called when cache has already been initialized,
+   * so only manipulate cache values when cache is pending. */
+  if (g_select_state.use_cache_needs_init) {
+    g_select_state.use_cache_needs_init = false;
+
+    switch (g_select_state.algorithm) {
+      case ALGO_GL_QUERY: {
+        g_select_state.use_cache = false;
+        break;
+      }
+      default: {
+        g_select_state.use_cache = true;
+        gpu_select_pick_cache_begin();
+        break;
+      }
+    }
+  }
+
   switch (g_select_state.algorithm) {
     case ALGO_GL_QUERY: {
-      g_select_state.use_cache = false;
       gpu_select_query_begin((uint(*)[4])buffer, bufsize / 4, input, mode, oldhits);
       break;
     }
@@ -154,12 +180,13 @@ uint GPU_select_end(void)
 
 void GPU_select_cache_begin(void)
 {
-  /* validate on GPU_select_begin, clear if not supported */
-  BLI_assert(g_select_state.use_cache == false);
-  g_select_state.use_cache = true;
-  if (g_select_state.algorithm == ALGO_GL_PICK) {
-    gpu_select_pick_cache_begin();
-  }
+  BLI_assert(g_select_state.select_is_active == false);
+  /* Ensure #GPU_select_cache_end is always called. */
+  BLI_assert(g_select_state.use_cache_needs_init == false);
+
+  /* Signal that cache should be used, instead of calling the algorithms cache-begin function.
+   * This is more convenient as the exact method of selection may not be known by the caller. */
+  g_select_state.use_cache_needs_init = true;
 }
 
 void GPU_select_cache_load_id(void)
@@ -173,9 +200,12 @@ void GPU_select_cache_load_id(void)
 void GPU_select_cache_end(void)
 {
   if (g_select_state.algorithm == ALGO_GL_PICK) {
+    BLI_assert(g_select_state.use_cache == true);
     gpu_select_pick_cache_end();
   }
   g_select_state.use_cache = false;
+  /* Paranoid assignment, should already be false. */
+  g_select_state.use_cache_needs_init = false;
 }
 
 bool GPU_select_is_cached(void)