GPU: UniformBuf: Add GPU_uniformbuf_clear_to_zero

This allows clearing the entire buffer directly on GPU.

source/blender/gpu/GPU_uniform_buffer.h

@@ -43,6 +43,8 @@ void GPU_uniformbuf_bind_as_ssbo(GPUUniformBuf *ubo, int slot);
 void GPU_uniformbuf_unbind(GPUUniformBuf *ubo);
 void GPU_uniformbuf_unbind_all(void);
 
+void GPU_uniformbuf_clear_to_zero(GPUUniformBuf *ubo);
+
 #define GPU_UBO_BLOCK_NAME "node_tree"
 #define GPU_ATTRIBUTE_UBO_BLOCK_NAME "unf_attrs"
 #define GPU_LAYER_ATTRIBUTE_UBO_BLOCK_NAME "drw_layer_attrs"

source/blender/gpu/intern/gpu_uniform_buffer.cc

@@ -233,4 +233,9 @@ void GPU_uniformbuf_unbind_all()
   /* FIXME */
 }
 
+void GPU_uniformbuf_clear_to_zero(GPUUniformBuf *ubo)
+{
+  unwrap(ubo)->clear_to_zero();
+}
+
 /** \} */

source/blender/gpu/intern/gpu_uniform_buffer_private.hh

@@ -38,6 +38,7 @@ class UniformBuf {
   virtual ~UniformBuf();
 
   virtual void update(const void *data) = 0;
+  virtual void clear_to_zero() = 0;
   virtual void bind(int slot) = 0;
   virtual void bind_as_ssbo(int slot) = 0;
   virtual void unbind() = 0;

source/blender/gpu/metal/mtl_uniform_buffer.mm

@@ -81,6 +81,14 @@ void MTLUniformBuf::update(const void *data)
   }
 }
 
+void MTLUniformBuf::clear_to_zero()
+{
+  /* TODO(fclem): Avoid another allocation and just do the clear on the GPU if possible. */
+  void *clear_data = calloc(size_in_bytes_);
+  this->update(clear_data);
+  free(clear_data);
+}
+
 void MTLUniformBuf::bind(int slot)
 {
   if (slot < 0) {

source/blender/gpu/opengl/gl_uniform_buffer.cc

@@ -10,6 +10,7 @@
 #include "gpu_context_private.hh"
 
 #include "gl_debug.hh"
+#include "gl_texture.hh"
 #include "gl_uniform_buffer.hh"
 
 namespace blender::gpu {
@@ -56,6 +57,35 @@ void GLUniformBuf::update(const void *data)
   glBindBuffer(GL_UNIFORM_BUFFER, 0);
 }
 
+void GLUniformBuf::clear_to_zero()
+{
+  if (ubo_id_ == 0) {
+    this->init();
+  }
+
+  uint32_t data = 0;
+  eGPUTextureFormat internal_format = GPU_R32UI;
+  eGPUDataFormat data_format = GPU_DATA_UINT;
+
+  if (GLContext::direct_state_access_support) {
+    glClearNamedBufferData(ubo_id_,
+                           to_gl_internal_format(internal_format),
+                           to_gl_data_format(internal_format),
+                           to_gl(data_format),
+                           &data);
+  }
+  else {
+    /* WATCH(@fclem): This should be ok since we only use clear outside of drawing functions. */
+    glBindBuffer(GL_UNIFORM_BUFFER, ubo_id_);
+    glClearBufferData(GL_UNIFORM_BUFFER,
+                      to_gl_internal_format(internal_format),
+                      to_gl_data_format(internal_format),
+                      to_gl(data_format),
+                      &data);
+    glBindBuffer(GL_UNIFORM_BUFFER, 0);
+  }
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */

source/blender/gpu/opengl/gl_uniform_buffer.hh

@@ -29,6 +29,7 @@ class GLUniformBuf : public UniformBuf {
   ~GLUniformBuf();
 
   void update(const void *data) override;
+  void clear_to_zero() override;
   void bind(int slot) override;
   void bind_as_ssbo(int slot) override;
   void unbind() override;

source/blender/gpu/vulkan/vk_uniform_buffer.cc

@@ -13,6 +13,10 @@ void VKUniformBuffer::update(const void * /*data*/)
 {
 }
 
+void VKUniformBuffer::clear_to_zero()
+{
+}
+
 void VKUniformBuffer::bind(int /*slot*/)
 {
 }

source/blender/gpu/vulkan/vk_uniform_buffer.hh

@@ -18,6 +18,7 @@ class VKUniformBuffer : public UniformBuf {
   }
 
   void update(const void *data) override;
+  void clear_to_zero() override;
   void bind(int slot) override;
   void bind_as_ssbo(int slot) override;
   void unbind() override;