GL: Framebuffer: Add support for empty framebuffer (no attachments)

This allows to reduce the memory footprint of very large framebuffers if
there is no need for any attachment.

5 files changed, 19 insertions, 3 deletions

diff --git a/source/blender/gpu/GPU_framebuffer.h b/source/blender/gpu/GPU_framebuffer.h
index 70ec7c19e7c..bdb384c16f1 100644
--- a/source/blender/gpu/GPU_framebuffer.h
+++ b/source/blender/gpu/GPU_framebuffer.h
@@ -189,6 +189,12 @@ void GPU_framebuffer_texture_layer_attach(
 void GPU_framebuffer_texture_cubeface_attach(
     GPUFrameBuffer *fb, GPUTexture *tex, int slot, int face, int mip);
 
+/**
+ * Default size is used if the framebuffer contains no attachments.
+ * It needs to be re-specified each time an attachment is added.
+ */
+void GPU_framebuffer_default_size(GPUFrameBuffer *gpu_fb, int width, int height);
+
 /* Frame-buffer operations. */
 
 /**
diff --git a/source/blender/gpu/intern/gpu_framebuffer.cc b/source/blender/gpu/intern/gpu_framebuffer.cc
index 8d93e49d588..4182ce75eac 100644
--- a/source/blender/gpu/intern/gpu_framebuffer.cc
+++ b/source/blender/gpu/intern/gpu_framebuffer.cc
@@ -368,6 +368,11 @@ void GPU_framebuffer_config_array(GPUFrameBuffer *gpu_fb,
   }
 }
 
+void GPU_framebuffer_default_size(GPUFrameBuffer *gpu_fb, int width, int height)
+{
+  unwrap(gpu_fb)->size_set(width, height);
+}
+
 /* ---------- Viewport & Scissor Region ----------- */
 
 void GPU_framebuffer_viewport_set(GPUFrameBuffer *gpu_fb, int x, int y, int width, int height)
diff --git a/source/blender/gpu/intern/gpu_framebuffer_private.hh b/source/blender/gpu/intern/gpu_framebuffer_private.hh
index 8cecc6b8b15..6e5d9518bfc 100644
--- a/source/blender/gpu/intern/gpu_framebuffer_private.hh
+++ b/source/blender/gpu/intern/gpu_framebuffer_private.hh
@@ -74,9 +74,9 @@ class FrameBuffer {
   /** Set of texture attachments to render to. DEPTH and DEPTH_STENCIL are mutually exclusive. */
   GPUAttachment attachments_[GPU_FB_MAX_ATTACHMENT];
   /** Is true if internal representation need to be updated. */
-  bool dirty_attachments_;
+  bool dirty_attachments_ = true;
   /** Size of attachment textures. */
-  int width_, height_;
+  int width_ = 0, height_ = 0;
   /** Debug name. */
   char name_[DEBUG_NAME_LEN];
   /** Frame-buffer state. */
diff --git a/source/blender/gpu/opengl/gl_framebuffer.cc b/source/blender/gpu/opengl/gl_framebuffer.cc
index bd9fba4250d..1ab22a16df4 100644
--- a/source/blender/gpu/opengl/gl_framebuffer.cc
+++ b/source/blender/gpu/opengl/gl_framebuffer.cc
@@ -207,6 +207,11 @@ void GLFrameBuffer::update_attachments()
     this->size_set(size[0], size[1]);
     srgb_ = (GPU_texture_format(attach.tex) == GPU_SRGB8_A8);
   }
+  else {
+    /* Empty frame-buffer. */
+    glFramebufferParameteri(GL_FRAMEBUFFER, GL_FRAMEBUFFER_DEFAULT_WIDTH, width_);
+    glFramebufferParameteri(GL_FRAMEBUFFER, GL_FRAMEBUFFER_DEFAULT_HEIGHT, height_);
+  }
 
   dirty_attachments_ = false;
 
diff --git a/source/blender/gpu/opengl/gl_framebuffer.hh b/source/blender/gpu/opengl/gl_framebuffer.hh
index 8ee04a584bd..edc05322153 100644
--- a/source/blender/gpu/opengl/gl_framebuffer.hh
+++ b/source/blender/gpu/opengl/gl_framebuffer.hh
@@ -32,7 +32,7 @@ class GLFrameBuffer : public FrameBuffer {
   /** State Manager of the same contexts. */
   GLStateManager *state_manager_ = nullptr;
   /** Copy of the GL state. Contains ONLY color attachments enums for slot binding. */
-  GLenum gl_attachments_[GPU_FB_MAX_COLOR_ATTACHMENT];
+  GLenum gl_attachments_[GPU_FB_MAX_COLOR_ATTACHMENT] = {0};
   /** Internal frame-buffers are immutable. */
   bool immutable_;
   /** True is the frame-buffer has its first color target using the GPU_SRGB8_A8 format. */