mesa/st: rework support for sRGB framebuffer attachements

For GLES sRGB framebuffer attachemnt support is provided in two steps:
sRGB attachments like described in EXT_sRGB (and GLES 3.0) that enable
linear to sRGB color space transformation automatically, and the ability
to switch formats of the render target surface between sRGB and linear
that introduces full support for EXT_framebuffer_sRGB.
Set the according flags to reflect these two levels of sRGB support.

As a difference between desktopm GL and GLES, on desktop GL for a sRGB
framebuffer attachment the linear-sRGB conversion is turned off by default,
and for GLES it is turned on. This needs to be taken into account when
initally creating a surface, i.e. on desktop GL creation of a sRGB surface
is preferred, but on GLES sRGB surfaces are only created when explicitely
requested.

v2: - Use the new CAPS name

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/mesa/state_tracker/st_cb_fbo.c

@@ -139,7 +139,7 @@ st_renderbuffer_alloc_storage(struct gl_context * ctx,
    /* If an sRGB framebuffer is unsupported, sRGB formats behave like linear
     * formats.
     */
-   if (!ctx->Extensions.EXT_framebuffer_sRGB) {
+   if (!ctx->Extensions.EXT_sRGB) {
       internalFormat = _mesa_get_linear_internalformat(internalFormat);
    }
 
@@ -662,7 +662,7 @@ st_validate_attachment(struct gl_context *ctx,
    /* If the encoding is sRGB and sRGB rendering cannot be enabled,
     * check for linear format support instead.
     * Later when we create a surface, we change the format to a linear one. */
-   if (!ctx->Extensions.EXT_framebuffer_sRGB &&
+   if (!ctx->Extensions.EXT_sRGB &&
        _mesa_get_format_color_encoding(texFormat) == GL_SRGB) {
       const mesa_format linearFormat = _mesa_get_srgb_format_linear(texFormat);
       format = st_mesa_format_to_pipe_format(st_context(ctx), linearFormat);

src/mesa/state_tracker/st_extensions.c

@@ -789,7 +789,7 @@ void st_init_extensions(struct pipe_screen *screen,
           PIPE_FORMAT_B10G10R10A2_UINT },
          GL_TRUE }, /* at least one format must be supported */
 
-      { { o(EXT_framebuffer_sRGB) },
+      { { o(EXT_sRGB) },
         { PIPE_FORMAT_A8B8G8R8_SRGB,
           PIPE_FORMAT_B8G8R8A8_SRGB,
           PIPE_FORMAT_R8G8B8A8_SRGB },
@@ -1327,6 +1327,10 @@ void st_init_extensions(struct pipe_screen *screen,
       extensions->ARB_texture_buffer_object_rgb32 &&
       extensions->ARB_shader_image_load_store;
 
+   extensions->EXT_framebuffer_sRGB =
+         screen->get_param(screen, PIPE_CAP_DEST_SURFACE_SRGB_CONTROL) &&
+         extensions->EXT_sRGB;
+
    /* Unpacking a varying in the fragment shader costs 1 texture indirection.
     * If the number of available texture indirections is very limited, then we
     * prefer to disable varying packing rather than run the risk of varying

src/mesa/state_tracker/st_format.c

@@ -2457,7 +2457,7 @@ st_QuerySamplesForFormat(struct gl_context *ctx, GLenum target,
    /* If an sRGB framebuffer is unsupported, sRGB formats behave like linear
     * formats.
     */
-   if (!ctx->Extensions.EXT_framebuffer_sRGB) {
+   if (!ctx->Extensions.EXT_sRGB) {
       internalFormat = _mesa_get_linear_internalformat(internalFormat);
    }
 

src/mesa/state_tracker/st_manager.c

@@ -305,7 +305,7 @@ st_framebuffer_update_attachments(struct st_framebuffer *stfb)
  */
 static boolean
 st_framebuffer_add_renderbuffer(struct st_framebuffer *stfb,
-                                gl_buffer_index idx)
+                                gl_buffer_index idx, bool prefer_srgb)
 {
    struct gl_renderbuffer *rb;
    enum pipe_format format;
@@ -328,7 +328,7 @@ st_framebuffer_add_renderbuffer(struct st_framebuffer *stfb,
       break;
    default:
       format = stfb->iface->visual->color_format;
-      if (stfb->Base.Visual.sRGBCapable)
+      if (prefer_srgb)
          format = util_format_srgb(format);
       sw = FALSE;
       break;
@@ -446,6 +446,7 @@ st_framebuffer_create(struct st_context *st,
    struct st_framebuffer *stfb;
    struct gl_config mode;
    gl_buffer_index idx;
+   bool prefer_srgb = false;
 
    if (!stfbi)
       return NULL;
@@ -467,14 +468,15 @@ st_framebuffer_create(struct st_context *st,
     * format such that util_format_srgb(visual->color_format) can be supported
     * by the pipe driver.  We still need to advertise the capability here.
     *
-    * For GLES, however, sRGB framebuffer write is controlled only by the
-    * capability of the framebuffer.  There is GL_EXT_sRGB_write_control to
-    * give applications the control back, but sRGB write is still enabled by
-    * default.  To avoid unexpected results, we should not advertise the
-    * capability.  This could change when we add support for
-    * EGL_KHR_gl_colorspace.
+    * For GLES, however, sRGB framebuffer write is initially only controlled
+    * by the capability of the framebuffer, with GL_EXT_sRGB_write_control
+    * control is given back to the applications, but GL_FRAMEBUFFER_SRGB is
+    * still enabled by default since this is the behaviour when
+    * EXT_sRGB_write_control is not available. Since GL_EXT_sRGB_write_control
+    * brings GLES on par with desktop GLs EXT_framebuffer_sRGB, in mesa this
+    * is also expressed by using the same extension flag
     */
-   if (_mesa_is_desktop_gl(st->ctx)) {
+   if (st->ctx->Extensions.EXT_framebuffer_sRGB) {
       struct pipe_screen *screen = st->pipe->screen;
       const enum pipe_format srgb_format =
          util_format_srgb(stfbi->visual->color_format);
@@ -485,8 +487,14 @@ st_framebuffer_create(struct st_context *st,
                                       PIPE_TEXTURE_2D, stfbi->visual->samples,
                                       stfbi->visual->samples,
                                       (PIPE_BIND_DISPLAY_TARGET |
-                                       PIPE_BIND_RENDER_TARGET)))
+                                       PIPE_BIND_RENDER_TARGET))) {
          mode.sRGBCapable = GL_TRUE;
+         /* Since GL_FRAMEBUFFER_SRGB is enabled by default on GLES we must not
+          * create renderbuffers with an sRGB format derived from the
+          * visual->color_format, but we still want sRGB for desktop GL.
+          */
+         prefer_srgb = _mesa_is_desktop_gl(st->ctx);
+      }
    }
 
    _mesa_initialize_window_framebuffer(&stfb->Base, &mode);
@@ -497,13 +505,13 @@ st_framebuffer_create(struct st_context *st,
 
    /* add the color buffer */
    idx = stfb->Base._ColorDrawBufferIndexes[0];
-   if (!st_framebuffer_add_renderbuffer(stfb, idx)) {
+   if (!st_framebuffer_add_renderbuffer(stfb, idx, prefer_srgb)) {
       free(stfb);
       return NULL;
    }
 
-   st_framebuffer_add_renderbuffer(stfb, BUFFER_DEPTH);
-   st_framebuffer_add_renderbuffer(stfb, BUFFER_ACCUM);
+   st_framebuffer_add_renderbuffer(stfb, BUFFER_DEPTH, false);
+   st_framebuffer_add_renderbuffer(stfb, BUFFER_ACCUM, false);
 
    stfb->stamp = 0;
    st_framebuffer_update_attachments(stfb);
@@ -1209,7 +1217,8 @@ st_manager_add_color_renderbuffer(struct st_context *st,
       return FALSE;
    }
 
-   if (!st_framebuffer_add_renderbuffer(stfb, idx))
+   if (!st_framebuffer_add_renderbuffer(stfb, idx,
+                                        stfb->Base.Visual.sRGBCapable))
       return FALSE;
 
    st_framebuffer_update_attachments(stfb);