WM: new offscreen window draw method to replace all existing methods.

For Blender 2.8 we had to be compatible with very old OpenGL versions, and
triple buffer was designed to work without offscreen rendering, by copying
the the backbuffer to a texture right before swapping. This way we could
avoid redrawing unchanged regions by copying them from this texture on the
next redraws. Triple buffer used to suffer from poor performance and driver
bugs on specific cards, so alternative draw methods remained available.

Now that we require newer OpenGL, we can have just a single draw method
that draw each region into an offscreen buffer, and then draws those to
the screen. This has some advantages:

* Poor 3D view performance when using Region Overlap should be solved now,
  since we can also cache overlapping regions in offscreen buffers.
* Page flip, anaglyph and interlace stereo drawing can be a little faster
  by avoiding a copy to an intermediate texture.
* The new 3D view drawing already writes to an offscreen buffer, which we
  can draw from directly instead of duplicating it to another buffer.
* Eventually we will be able to remove depth and stencil buffers from the
  window and save memory, though at the moment there are still some tools
  using it so it's not possible yet.
* This also fixes a bug with Eevee sampling not progressing with stereo
  drawing in the 3D viewport.

Differential Revision: https://developer.blender.org/D3061

5 files changed, 41 insertions, 3 deletions

diff --git a/source/blender/gpu/GPU_framebuffer.h b/source/blender/gpu/GPU_framebuffer.h
index c99733ec6da..61dd899f3d9 100644
--- a/source/blender/gpu/GPU_framebuffer.h
+++ b/source/blender/gpu/GPU_framebuffer.h
@@ -185,6 +185,7 @@ void GPU_offscreen_free(GPUOffScreen *ofs);
 void GPU_offscreen_bind(GPUOffScreen *ofs, bool save);
 void GPU_offscreen_unbind(GPUOffScreen *ofs, bool restore);
 void GPU_offscreen_read_pixels(GPUOffScreen *ofs, int type, void *pixels);
+void GPU_offscreen_draw_to_screen(GPUOffScreen *ofs, int x, int y);
 int GPU_offscreen_width(const GPUOffScreen *ofs);
 int GPU_offscreen_height(const GPUOffScreen *ofs);
 struct GPUTexture *GPU_offscreen_color_texture(const GPUOffScreen *ofs);
diff --git a/source/blender/gpu/GPU_viewport.h b/source/blender/gpu/GPU_viewport.h
index ca7d5ae7ceb..d63911374ae 100644
--- a/source/blender/gpu/GPU_viewport.h
+++ b/source/blender/gpu/GPU_viewport.h
@@ -119,6 +119,8 @@ double *GPU_viewport_cache_time_get(GPUViewport *viewport);
 void GPU_viewport_tag_update(GPUViewport *viewport);
 bool GPU_viewport_do_update(GPUViewport *viewport);
 
+GPUTexture *GPU_viewport_color_texture(GPUViewport *viewport);
+
 /* Texture pool */
 GPUTexture *GPU_viewport_texture_pool_query(GPUViewport *viewport, void *engine, int width, int height, int channels, int format);
 
diff --git a/source/blender/gpu/intern/gpu_framebuffer.c b/source/blender/gpu/intern/gpu_framebuffer.c
index 73a1f14b9f6..3f89adfd8a5 100644
--- a/source/blender/gpu/intern/gpu_framebuffer.c
+++ b/source/blender/gpu/intern/gpu_framebuffer.c
@@ -719,6 +719,24 @@ void GPU_offscreen_unbind(GPUOffScreen *UNUSED(ofs), bool restore)
 	}
 }
 
+void GPU_offscreen_draw_to_screen(GPUOffScreen *ofs, int x, int y)
+{
+	const int w = GPU_texture_width(ofs->color);
+	const int h = GPU_texture_height(ofs->color);
+
+	glBindFramebuffer(GL_READ_FRAMEBUFFER, ofs->fb->object);
+	GLenum status = glCheckFramebufferStatus(GL_READ_FRAMEBUFFER);
+
+	if (status == GL_FRAMEBUFFER_COMPLETE) {
+		glBlitFramebuffer(0, 0, w, h, x, y, x + w, y + h, GL_COLOR_BUFFER_BIT, GL_NEAREST);
+	}
+	else {
+		gpu_print_framebuffer_error(status, NULL);
+	}
+
+	glBindFramebuffer(GL_READ_FRAMEBUFFER, 0);
+}
+
 void GPU_offscreen_read_pixels(GPUOffScreen *ofs, int type, void *pixels)
 {
 	const int w = GPU_texture_width(ofs->color);
diff --git a/source/blender/gpu/intern/gpu_shader.c b/source/blender/gpu/intern/gpu_shader.c
index 609aa529872..34dee37001e 100644
--- a/source/blender/gpu/intern/gpu_shader.c
+++ b/source/blender/gpu/intern/gpu_shader.c
@@ -714,8 +714,6 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 		                                           datatoc_gpu_shader_image_desaturate_frag_glsl },
 		[GPU_SHADER_2D_IMAGE_ALPHA_COLOR] = { datatoc_gpu_shader_2D_image_vert_glsl,
 		                                      datatoc_gpu_shader_image_alpha_color_frag_glsl },
-		[GPU_SHADER_2D_IMAGE_ALPHA] = { datatoc_gpu_shader_2D_image_vert_glsl,
-		                                datatoc_gpu_shader_image_modulate_alpha_frag_glsl },
 		[GPU_SHADER_2D_IMAGE_SHUFFLE_COLOR] = { datatoc_gpu_shader_2D_image_vert_glsl,
 		                                        datatoc_gpu_shader_image_shuffle_color_frag_glsl },
 		[GPU_SHADER_2D_IMAGE_RECT_COLOR] = { datatoc_gpu_shader_2D_image_rect_vert_glsl,
diff --git a/source/blender/gpu/intern/gpu_viewport.c b/source/blender/gpu/intern/gpu_viewport.c
index 5d89bd59277..383ebec5b72 100644
--- a/source/blender/gpu/intern/gpu_viewport.c
+++ b/source/blender/gpu/intern/gpu_viewport.c
@@ -38,6 +38,8 @@
 #include "BLI_string.h"
 #include "BLI_mempool.h"
 
+#include "BIF_gl.h"
+
 #include "DNA_vec_types.h"
 #include "DNA_userdef_types.h"
 
@@ -521,6 +523,10 @@ void GPU_viewport_draw_to_screen(GPUViewport *viewport, const rcti *rect)
 	BLI_assert(w == BLI_rcti_size_x(rect) + 1);
 	BLI_assert(h == BLI_rcti_size_y(rect) + 1);
 
+	/* wmOrtho for the screen has this same offset */
+	const float halfx = GLA_PIXEL_OFS / w;
+	const float halfy = GLA_PIXEL_OFS / h;
+
 	float x1 = rect->xmin;
 	float x2 = rect->xmin + w;
 	float y1 = rect->ymin;
@@ -531,7 +537,7 @@ void GPU_viewport_draw_to_screen(GPUViewport *viewport, const rcti *rect)
 
 	GPU_texture_bind(color, 0);
 	glUniform1i(GPU_shader_get_uniform(shader, "image"), 0);
-	glUniform4f(GPU_shader_get_uniform(shader, "rect_icon"), 0.0f, 0.0f, 1.0f, 1.0f);
+	glUniform4f(GPU_shader_get_uniform(shader, "rect_icon"), halfx, halfy, 1.0f + halfx, 1.0f + halfy);
 	glUniform4f(GPU_shader_get_uniform(shader, "rect_geom"), x1, y1, x2, y2);
 	glUniform4f(GPU_shader_get_builtin_uniform(shader, GWN_UNIFORM_COLOR), 1.0f, 1.0f, 1.0f, 1.0f);
 
@@ -545,6 +551,19 @@ void GPU_viewport_unbind(GPUViewport *UNUSED(viewport))
 	DRW_opengl_context_disable();
 }
 
+
+GPUTexture *GPU_viewport_color_texture(GPUViewport *viewport)
+{
+	DefaultFramebufferList *dfbl = viewport->fbl;
+
+	if (dfbl->default_fb) {
+		DefaultTextureList *dtxl = viewport->txl;
+		return dtxl->color;
+	}
+
+	return NULL;
+}
+
 static void gpu_viewport_buffers_free(
         FramebufferList *fbl, int fbl_len,
         TextureList *txl, int txl_len)