GPUShader: Implement workaround for gizmo drawing on sRGB framebuffer

This solution involves adding a uniform to each fragment shader that is
used by gizmo drawing and use the framebuffer state to set this uniform
accordingly.

This solution can also be carried to external shaders (addons).
A single line of code would then be enough to fix the issue.

The only trickery here is the dummy define:
`#define srgb_to_framebuffer_space(a)`
This is in order to avoid breaking other DRW shaders that use the same
fragment shader code but do not need the tranformation.

Related to T74139

Reviewed By: brecht, campbellbarton

Differential Revision: https://developer.blender.org/D7261

1 files changed, 1 insertions, 1 deletions

diff --git a/source/blender/editors/space_image/space_image.c b/source/blender/editors/space_image/space_image.c
index af94b5b6e21..1e1d4373fea 100644
--- a/source/blender/editors/space_image/space_image.c
+++ b/source/blender/editors/space_image/space_image.c
@@ -653,13 +653,13 @@ static void image_main_region_draw(const bContext *C, ARegion *region)
   GPU_clear(GPU_COLOR_BIT);
 
   GPU_framebuffer_bind(fbl->overlay_fb);
-  glDisable(GL_FRAMEBUFFER_SRGB);
 
   /* XXX not supported yet, disabling for now */
   scene->r.scemode &= ~R_COMP_CROP;
 
   /* clear and setup matrix */
   UI_GetThemeColor3fv(TH_BACK, col);
+  srgb_to_linearrgb_v3_v3(col, col);
   GPU_clear_color(col[0], col[1], col[2], 1.0f);
   GPU_clear(GPU_COLOR_BIT);
   GPU_depth_test(false);