GLTexture: Add validation for empty slots before drawing

This is to have better error detection in debug builds.
This is not a replacement for a full check like in renderdoc but it
might catch some issues early on.

source/blender/gpu/intern/gpu_shader_interface.hh

@@ -93,6 +93,11 @@ class ShaderInterface {
     return input_lookup(inputs_ + attr_len_ + ubo_len_, uniform_len_, name);
   }
 
+  inline const ShaderInput *texture_get(const int binding) const
+  {
+    return input_lookup(inputs_ + attr_len_ + ubo_len_, uniform_len_, binding);
+  }
+
   inline const char *input_name_get(const ShaderInput *input) const
   {
     return name_buffer_ + input->name_offset;

source/blender/gpu/opengl/gl_debug.cc

@@ -186,7 +186,12 @@ void check_gl_resources(const char *info)
   uint16_t ubo_needed = interface->enabled_ubo_mask_;
   ubo_needed &= ~ctx->bound_ubo_slots;
 
-  if (ubo_needed == 0) {
+  /* NOTE: This only check binding. To be valid, the bound texture needs to
+   * be the same format/target the shader expects. */
+  uint64_t tex_needed = interface->enabled_tex_mask_;
+  tex_needed &= ~ctx->state_manager_active_get()->bound_texture_slots();
+
+  if (ubo_needed == 0 && tex_needed == 0) {
     return;
   }
 
@@ -200,6 +205,17 @@ void check_gl_resources(const char *info)
       debug_callback(0, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, 0, msg, NULL);
     }
   }
+
+  for (int i = 0; tex_needed != 0; i++, tex_needed >>= 1) {
+    if ((tex_needed & 1) != 0) {
+      const ShaderInput *tex_input = interface->texture_get(i);
+      const char *tex_name = interface->input_name_get(tex_input);
+      const char *sh_name = ctx->shader->name_get();
+      char msg[256];
+      SNPRINTF(msg, "Missing Texture bind at slot %d : %s > %s : %s", i, sh_name, tex_name, info);
+      debug_callback(0, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, 0, msg, NULL);
+    }
+  }
 }
 
 void raise_gl_error(const char *msg)

source/blender/gpu/opengl/gl_state.cc

@@ -503,6 +503,17 @@ void GLStateManager::texture_bind_apply(void)
   }
 }
 
+uint64_t GLStateManager::bound_texture_slots(void)
+{
+  uint64_t bound_slots = 0;
+  for (int i = 0; i < ARRAY_SIZE(textures_); i++) {
+    if (textures_[i] != 0) {
+      bound_slots |= 1 << i;
+    }
+  }
+  return bound_slots;
+}
+
 /** \} */
 
 }  // namespace blender::gpu

source/blender/gpu/opengl/gl_state.hh

@@ -74,6 +74,8 @@ class GLStateManager : public GPUStateManager {
   void texture_unbind(Texture *tex) override;
   void texture_unbind_all(void) override;
 
+  uint64_t bound_texture_slots(void);
+
  private:
   static void set_write_mask(const eGPUWriteMask value);
   static void set_depth_test(const eGPUDepthTest value);