GPUFrameBuffer: GL backend isolation

This is related to the Vulkan port T68990.

This is a full cleanup of the Framebuffer module and a separation
of OpenGL related functions.

There is some changes with how the default framebuffers are handled.
Now the default framebuffers are individually wrapped inside special
GLFrameBuffers. This make it easier to keep track of the currently bound
framebuffer state and have some specificity for operations on these
framebuffers.

Another change is dropping the optimisation of only configuring the
changed attachements during framebuffers update. This does not give
any benefits and add some complexity to the code. This might be brought
back if it has a performance impact on some systems.

This also adds support for naming framebuffers but it is currently not
used.

1 files changed, 142 insertions, 0 deletions

diff --git a/source/blender/gpu/opengl/gl_framebuffer.hh b/source/blender/gpu/opengl/gl_framebuffer.hh
new file mode 100644
index 00000000000..a83bc1f6cae
--- /dev/null
+++ b/source/blender/gpu/opengl/gl_framebuffer.hh
@@ -0,0 +1,142 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2020 Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup gpu
+ *
+ * Encapsulation of Framebuffer states (attached textures, viewport, scissors).
+ */
+
+#pragma once
+
+#include "MEM_guardedalloc.h"
+
+#include "glew-mx.h"
+
+#include "gpu_framebuffer_private.hh"
+
+namespace blender::gpu {
+
+/**
+ * Implementation of FrameBuffer object using OpenGL.
+ **/
+class GLFrameBuffer : public FrameBuffer {
+ private:
+  /** OpenGL handle. */
+  GLuint fbo_id_ = 0;
+  /** Context the handle is from. Framebuffers are not shared accros contexts. */
+  GLContext *context_ = NULL;
+  /** Copy of the GL state. Contains ONLY color attachments enums for slot binding. */
+  GLenum gl_attachments_[GPU_FB_MAX_COLOR_ATTACHMENT];
+  /** Internal framebuffers are immutable. */
+  bool immutable_;
+  /** True is the framebuffer has it's first color target using the GPU_SRGB8_A8 format. */
+  bool srgb_;
+
+ public:
+  /**
+   * Create a conventional framebuffer to attach texture to.
+   **/
+  GLFrameBuffer(const char *name);
+
+  /**
+   * Special Framebuffer encapsulating internal window framebuffer.
+   *  (i.e.: GL_FRONT_LEFT, GL_BACK_RIGHT, ...)
+   * @param ctx     context the handle is from.
+   * @param target  the internal GL name (i.e: GL_BACK_LEFT).
+   * @param fbo     the (optional) already created object for some implementation. Default is 0.
+   * @param w       buffer width.
+   * @param h       buffer height.
+   **/
+  GLFrameBuffer(const char *name, GLContext *ctx, GLenum target, GLuint fbo, int w, int h);
+
+  ~GLFrameBuffer();
+
+  void bind(bool enabled_srgb) override;
+
+  bool check(char err_out[256]) override;
+
+  void clear(eGPUFrameBufferBits buffers,
+             const float clear_col[4],
+             float clear_depth,
+             uint clear_stencil) override;
+  void clear_multi(const float (*clear_cols)[4]) override;
+
+  void read(eGPUFrameBufferBits planes,
+            eGPUDataFormat format,
+            const int area[4],
+            int channel_len,
+            int slot,
+            void *r_data) override;
+
+  void blit_to(eGPUFrameBufferBits planes,
+               int src_slot,
+               FrameBuffer *dst,
+               int dst_slot,
+               int dst_offset_x,
+               int dst_offset_y) override;
+
+ private:
+  void init(void);
+  void update_attachments(void);
+  void update_drawbuffers(void);
+
+  MEM_CXX_CLASS_ALLOC_FUNCS("GLFrameBuffer");
+};
+
+/* -------------------------------------------------------------------- */
+/** \name Enums Conversion
+ * \{ */
+
+static inline GLenum to_gl(const GPUAttachmentType type)
+{
+#define ATTACHMENT(X) \
+  case GPU_FB_##X: { \
+    return GL_##X; \
+  } \
+    ((void)0)
+
+  switch (type) {
+    ATTACHMENT(DEPTH_ATTACHMENT);
+    ATTACHMENT(DEPTH_STENCIL_ATTACHMENT);
+    ATTACHMENT(COLOR_ATTACHMENT0);
+    ATTACHMENT(COLOR_ATTACHMENT1);
+    ATTACHMENT(COLOR_ATTACHMENT2);
+    ATTACHMENT(COLOR_ATTACHMENT3);
+    ATTACHMENT(COLOR_ATTACHMENT4);
+    ATTACHMENT(COLOR_ATTACHMENT5);
+    default:
+      BLI_assert(0);
+      return GL_COLOR_ATTACHMENT0;
+  }
+#undef ATTACHMENT
+}
+
+static inline GLbitfield to_gl(const eGPUFrameBufferBits bits)
+{
+  GLbitfield mask = 0;
+  mask |= (bits & GPU_DEPTH_BIT) ? GL_DEPTH_BUFFER_BIT : 0;
+  mask |= (bits & GPU_STENCIL_BIT) ? GL_STENCIL_BUFFER_BIT : 0;
+  mask |= (bits & GPU_COLOR_BIT) ? GL_COLOR_BUFFER_BIT : 0;
+  return mask;
+}
+
+/** \} */
+
+}  // namespace blender::gpu