GL: add ES-only TextureFormat::BGRA[8].

And clarify their purpose. This was an accidental ommision, as there's
no need for such a thing on desktop.

doc/changelog.dox

@@ -123,6 +123,8 @@ See also:
     @gl_extension{EXT,texture_sRGB_RG8} extensions adding
     @ref GL::TextureFormat::SR8 and @ref GL::TextureFormat::SRG8 formats to
     complement new sRGB formats in @ref GL::PixelFormat
+-   Added ES-only @ref GL::TextureFormat::BGRA and @ref GL::TextureFormat::BGRA8
+    and clarified their purpose in relation to @ref GL::PixelFormat::BGRA
 -   New @ref GL::AbstractFramebuffer::implementationColorReadFormat() and
     @ref GL::AbstractFramebuffer::implementationColorReadType() queries for
     more robust checks when doing framebuffer readbacks; together with three

src/Magnum/GL/AbstractTexture.cpp

@@ -821,6 +821,12 @@ PixelFormat pixelFormatForInternalFormat(const TextureFormat internalFormat) {
             return PixelFormat::SRGBAlpha;
             #endif
 
+        #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
+        case TextureFormat::BGRA:
+        case TextureFormat::BGRA8:
+            return PixelFormat::BGRA;
+        #endif
+
         #ifndef MAGNUM_TARGET_GLES2
         case TextureFormat::RGBA8UI:
         case TextureFormat::RGBA8I:
@@ -919,6 +925,12 @@ PixelType pixelTypeForInternalFormat(const TextureFormat internalFormat) {
         #endif
         #ifndef MAGNUM_TARGET_GLES
         case TextureFormat::RGBA2: /**< @todo really? */
+        #endif
+        #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
+        case TextureFormat::BGRA:
+        case TextureFormat::BGRA8:
+        #endif
+        #ifndef MAGNUM_TARGET_GLES
         case TextureFormat::CompressedRed:
         case TextureFormat::CompressedRG:
         case TextureFormat::CompressedRGB:

src/Magnum/GL/PixelFormat.h

@@ -143,16 +143,22 @@ enum class PixelFormat: GLenum {
 
     #ifndef MAGNUM_TARGET_GLES
     /**
-     * Floating-point BGR.
-     * @requires_gl Only RGB component ordering is available in OpenGL ES and
-     *      WebGL.
+     * Floating-point BGR. On desktop OpenGL there's no corresponding dedicated
+     * texture format for BGR(A) --- simply use it with @ref TextureFormat::RGB8.
+     * @requires_gl For three-component formats, only RGB component ordering is
+     *      available in OpenGL ES and WebGL. See @ref PixelFormat::BGRA for an
+     *      alternative.
      */
     BGR = GL_BGR,
     #endif
 
     #ifndef MAGNUM_TARGET_WEBGL
     /**
-     * Floating-point BGRA.
+     * Floating-point BGRA. On desktop OpenGL there's no corresponding
+     * dedicated texture format for BGR(A) --- simply use it with
+     * @ref TextureFormat::RGBA8. On OpenGL ES however, you're required to
+     * use @ref TextureFormat::BGRA8 (which is on the other hand not defined
+     * for desktop OpenGL).
      * @requires_es_extension Extension @gl_extension{EXT,read_format_bgra}
      *      for framebuffer reading, extension @gl_extension{APPLE,texture_format_BGRA8888}
      *      or @gl_extension{EXT,texture_format_BGRA8888} for texture data.

src/Magnum/GL/TextureFormat.cpp

@@ -163,6 +163,10 @@ Debug& operator<<(Debug& debug, const TextureFormat value) {
         #ifndef MAGNUM_TARGET_GLES
         _c(RGBA12)
         #endif
+        #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
+        _c(BGRA)
+        _c(BGRA8)
+        #endif
         #ifndef MAGNUM_TARGET_GLES
         _c(CompressedRed)
         _c(CompressedRG)

src/Magnum/GL/TextureFormat.h

@@ -129,7 +129,9 @@ enum class TextureFormat: GLenum {
     /**
      * RGB, type/size implementation-dependent. Not allowed in unemulated
      * @ref Texture::setStorage() "*Texture::setStorage()" calls, in
-     * that case use @ref TextureFormat::RGB8 "TextureFormat::RGB8" instead.
+     * that case use @ref TextureFormat::RGB8 "TextureFormat::RGB8" instead. On
+     * desktop OpenGL this format is meant to be used for
+     * @ref PixelFormat::BGR as well.
      * @requires_gl Can't be used as a render target in OpenGL ES or WebGL. See
      *      @ref TextureFormat::RGBA for an alternative.
      * @deprecated_gl Prefer to use the exactly specified version of this
@@ -142,7 +144,8 @@ enum class TextureFormat: GLenum {
 
     #if !(defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2))
     /**
-     * RGB, each component normalized unsigned byte.
+     * RGB, each component normalized unsigned byte. On desktop OpenGL this
+     * format is meant to be used for @ref PixelFormat::BGRA as well.
      * @requires_gles30 Extension @gl_extension{OES,required_internalformat}
      *      (for image specification) or @gl_extension{EXT,texture_storage}
      *      (for texture storage) in OpenGL ES 2.0. Use @ref TextureFormat::RGB
@@ -160,7 +163,10 @@ enum class TextureFormat: GLenum {
     /**
      * RGBA, type/size implementation-dependent. Not allowed in unemulated
      * @ref Texture::setStorage() "*Texture::setStorage()" calls, in that case
-     * use @ref TextureFormat::RGBA8 "TextureFormat::RGBA8" instead.
+     * use @ref TextureFormat::RGBA8 "TextureFormat::RGBA8" instead. On desktop
+     * OpenGL this format is meant to be used for @ref PixelFormat::BGRA as
+     * well, however on OpenGL ES you're required to use
+     * @ref TextureFormat::BGRA for BGRA pixel formats.
      * @deprecated_gl Prefer to use the exactly specified version of this
      *      format, e.g. @ref TextureFormat::RGBA8.
      * @requires_webgl20 Extension @webgl_extension{OES,texture_half_float_linear}
@@ -171,7 +177,10 @@ enum class TextureFormat: GLenum {
 
     #if !(defined(MAGNUM_TARGET_WEBGL) && defined(MAGNUM_TARGET_GLES2))
     /**
-     * RGBA, each component normalized unsigned byte.
+     * RGBA, each component normalized unsigned byte. On desktop OpenGL this
+     * format is meant to be used with @ref PixelFormat::BGRA as well, however
+     * on OpenGL ES you're required to use @ref TextureFormat::BGRA8 for BGRA
+     * pixel formats.
      * @requires_gles30 Extension @gl_extension{OES,required_internalformat}
      *      (for image specification) or @gl_extension{EXT,texture_storage}
      *      (for texture storage) in OpenGL ES 2.0. Use @ref TextureFormat::RGBA
@@ -1018,6 +1027,34 @@ enum class TextureFormat: GLenum {
     RGBA12 = GL_RGBA12,
     #endif
 
+    #if defined(DOXYGEN_GENERATING_OUTPUT) || (defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL))
+    /**
+     * BGRA, type/size implementation-dependent. Not allowed in unemulated
+     * @ref Texture::setStorage() "*Texture::setStorage()" calls, in that case
+     * use @ref TextureFormat::RGBA8 "TextureFormat::RGBA8" instead.
+     * @deprecated_gl Prefer to use the exactly specified version of this
+     *      format, e.g. @ref TextureFormat::BGRA8.
+     * @requires_gles Not available on desktop OpenGL -- there it's perfectly
+     *      legal to use @ref TextureFormat::RGBA in combination with
+     *      @ref PixelFormat::BGRA.
+     * @requires_es_extension Extension @gl_extension{APPLE,texture_format_BGRA8888}
+     *      or @gl_extension{EXT,texture_format_BGRA8888}
+     * @requires_gles Only RGBA component ordering is available in WebGL.
+     */
+    BGRA = GL_BGRA_EXT,
+
+    /**
+     * BGRA, each component normalized unsigned byte.
+     * @requires_gles Not available on desktop OpenGL -- there it's perfectly
+     *      legal to use @ref TextureFormat::RGBA8 in combination with
+     *      @ref PixelFormat::BGRA.
+     * @requires_es_extension Extension @gl_extension{APPLE,texture_format_BGRA8888}. There are no signed
+     *      normalized, integral or floating-point types with BGRA ordering.
+     * @requires_gles Only RGBA component ordering is available in WebGL.
+     */
+    BGRA8 = GL_BGRA8_EXT,
+    #endif
+
     #ifndef MAGNUM_TARGET_GLES
     /**
      * Compressed red channel, normalized unsigned. **Not available on