GL: clarify use of sRGB formats on ES.

src/Magnum/GL/AbstractTexture.cpp

@@ -658,7 +658,7 @@ PixelFormat pixelFormatForInternalFormat(const TextureFormat internalFormat) {
         #if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_GLES2)
         case TextureFormat::SRGB:
         #endif
-        #if !(defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2))
+        #ifndef MAGNUM_TARGET_GLES2
         case TextureFormat::SRGB8:
         #endif
             #ifndef MAGNUM_TARGET_GLES2
@@ -838,8 +838,10 @@ PixelType pixelTypeForInternalFormat(const TextureFormat internalFormat) {
         case TextureFormat::SRGB:
         case TextureFormat::SRGBAlpha:
         #endif
-        #if !(defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2))
+        #ifndef MAGNUM_TARGET_GLES2
         case TextureFormat::SRGB8:
+        #endif
+        #if !(defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2))
         case TextureFormat::SRGB8Alpha8:
         #endif
         #ifndef MAGNUM_TARGET_GLES

src/Magnum/GL/RenderbufferFormat.h

@@ -514,6 +514,10 @@ enum class RenderbufferFormat: GLenum {
     RGB10A2UI = GL_RGB10_A2UI,
     #endif
 
+    /* NV_sRGB_formats makes GL_SRGB8_NV accepted here but since that format
+       doesn't make sense anywhere else and there's GL_SRGB8_ALPHA8_EXT anyway,
+       I don't think it's worth supporting. */
+
     /**
      * sRGBA, each component normalized unsigned byte.
      * @requires_gles30 Extension @gl_extension{EXT,sRGB} in OpenGL ES 2.0.

src/Magnum/GL/Test/TextureGLTest.cpp

@@ -2906,15 +2906,11 @@ void TextureGLTest::srgbStorage() {
 
     MAGNUM_VERIFY_NO_GL_ERROR();
 
-    texture.setStorage(1,
-        #if !(defined(MAGNUM_TARGET_GLES2) && defined(MAGNUM_TARGET_WEBGL))
-        TextureFormat::SRGB8,
-        #else
-        TextureFormat::SRGB,
-        #endif
-        Vector2i{32});
+    #ifndef MAGNUM_TARGET_GLES2
+    texture.setStorage(1, TextureFormat::SRGB8, Vector2i{32});
 
     MAGNUM_VERIFY_NO_GL_ERROR();
+    #endif
 }
 
 void TextureGLTest::srgbAlphaStorage() {

src/Magnum/GL/TextureFormat.h

@@ -863,22 +863,15 @@ enum class TextureFormat: GLenum {
     #endif
     #endif
 
-    #if !(defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2))
+    #ifndef MAGNUM_TARGET_GLES2
     /**
      * sRGB, each component normalized unsigned byte.
-     * @requires_gles30 Extension @gl_extension{EXT,sRGB} and
-     *      @gl_extension{EXT,texture_storage}, only for
-     *      @ref Texture::setStorage() "*Texture::setStorage()" calls,
-     *      otherwise use @ref TextureFormat::SRGB in OpenGL ES 2.0 instead.
+     * @requires_gles30 Use @ref TextureFormat::SRGB in OpenGL ES 2.0 instead.
      * @requires_gl Can't be used as render target in OpenGL ES. Use
      *      @ref TextureFormat::SRGB8Alpha8 instead.
      * @requires_webgl20 Use @ref TextureFormat::SRGB in WebGL 1.0 instead.
      */
-    #ifndef MAGNUM_TARGET_GLES2
-    SRGB8 = GL_SRGB8,
-    #else
-    SRGB8 = 0x8C41, /* Not in any spec, but seems to work at least on NV */
-    #endif
+    SRGB8 = GL_SRGB8, /* NV_sRGB_formats has this on ES2, but meh */
     #endif
 
     #ifndef MAGNUM_TARGET_GLES