GL: added BufferTexture::size().

Why the heck was it not here? Did I fear GL errors too much?

doc/changelog.dox

@@ -123,6 +123,8 @@ See also:
     and @cpp "mesa-implementation-color-read-format-dsa-explicit-binding" @ce,
     because it's 2019 and GL drivers are *still* awful. See
     @ref opengl-workarounds for more information.
+-   Added @ref GL::BufferTexture::size() as it was the only texture type were
+    this query was missing.
 -   New @cpp "swiftshader-no-es2-draw-instanced-entrypoints" @ce and
     @cpp "swiftshader-no-es2-oes-texture-3d-entrypoints" @ce workarounds
     disabling @gl_extension{ANGLE,instanced_arrays} and
@@ -190,7 +192,6 @@ See also:
     @ref BasicMutableImageView "MutableImageView*D" and
     @ref BasicMutableCompressedImageView "MutableCompressedImageView*D" as well
 
-
 @subsubsection changelog-latest-new-math Math library
 
 -   @ref Math::Frustum::begin() / @ref Math::Frustum::end() accessors for

doc/opengl-mapping.dox

@@ -227,7 +227,7 @@ OpenGL function                         | Matching API
 @fn_gl{GetSubroutineUniformLocation}    | |
 @fn_gl{GetSync}                         | |
 @fn_gl{GetTexImage}, \n `glGetnTexImage()`, \n @fn_gl_extension{GetnTexImage,ARB,robustness}, \n `glGetTextureImage()` | @ref GL::Texture::image(), \n @ref GL::TextureArray::image(), \n @ref GL::CubeMapTexture::image(), \n @ref GL::CubeMapTextureArray::image(), \n @ref GL::RectangleTexture::image()
-@fn_gl{GetTexLevelParameter}, \n `glGetTextureLevelParameter()` | @ref GL::Texture::imageSize(), \n @ref GL::TextureArray::imageSize(), \n @ref GL::CubeMapTexture::imageSize(), \n @ref GL::CubeMapTextureArray::imageSize(), \n @ref GL::RectangleTexture::imageSize()
+@fn_gl{GetTexLevelParameter}, \n `glGetTextureLevelParameter()` | @ref GL::Texture::imageSize(), \n @ref GL::TextureArray::imageSize(), \n @ref GL::CubeMapTexture::imageSize(), \n @ref GL::CubeMapTextureArray::imageSize(), \n @ref GL::RectangleTexture::imageSize(), \n @ref GL::BufferTexture::imageSize()
 @fn_gl{GetTexParameter}, \n `glGetTextureParameter()` | |
 @fn_gl_extension{GetTextureHandle,ARB,bindless_texture} | |
 @fn_gl_extension{GetTextureSamplerHandle,ARB,bindless_texture} | |

src/Magnum/GL/BufferTexture.cpp

@@ -70,6 +70,14 @@ Int BufferTexture::offsetAlignment() {
     return value;
 }
 
+Int BufferTexture::size() {
+    /* Can't use DataHelper<1>::imageSize(*this, 0)[0] because for 1D textures
+       it's not defined on ES */
+    Int size;
+    (this->*Context::current().state().texture->getLevelParameterivImplementation)(0, GL_TEXTURE_WIDTH, &size);
+    return size;
+}
+
 BufferTexture& BufferTexture::setBuffer(const BufferTextureFormat internalFormat, Buffer& buffer) {
     (this->*Context::current().state().texture->setBufferImplementation)(internalFormat, buffer);
     return *this;

src/Magnum/GL/BufferTexture.h

@@ -156,6 +156,23 @@ class MAGNUM_GL_EXPORT BufferTexture: public AbstractTexture {
         /** @brief Move assignment */
         BufferTexture& operator=(BufferTexture&&) noexcept = default;
 
+        /**
+         * @brief Texture size
+         *
+         * Equivalent to size of the buffer attached to @ref setBuffer()
+         * divided by size of a particular @ref BufferTextureFormat. The result
+         * is not cached in any way. If @gl_extension{ARB,direct_state_access}
+         * (part of OpenGL 4.5) is not available, the texture is bound before
+         * the operation (if not already).
+         * @see @fn_gl2_keyword{GetTextureLevelParameter,GetTexLevelParameter},
+         *      eventually @fn_gl{ActiveTexture}, @fn_gl{BindTexture} and
+         *      @fn_gl_keyword{GetTexLevelParameter} with
+         *      @def_gl_keyword{TEXTURE_WIDTH}
+         * @requires_gles31 Texture image size queries are not available in
+         *      OpenGL ES 3.0 and older.
+         */
+        Int size();
+
         /**
          * @brief Bind texture to given image unit
          * @param imageUnit Image unit

src/Magnum/GL/Test/BufferTextureGLTest.cpp

@@ -181,7 +181,16 @@ void BufferTextureGLTest::setBuffer() {
         0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
     };
     buffer.setData(data, BufferUsage::StaticDraw);
-    texture.setBuffer(BufferTextureFormat::R8UI, buffer);
+    texture.setBuffer(BufferTextureFormat::RG8UI, buffer);
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
+    #ifdef MAGNUM_TARGET_GLES
+    if(!Context::current().isVersionSupported(Version::GLES310))
+        CORRADE_SKIP("OpenGL ES 3.1 not supported, skipping image size testing.");
+    #endif
+
+    CORRADE_COMPARE(texture.size(), 8);
 
     MAGNUM_VERIFY_NO_GL_ERROR();
 }
@@ -210,7 +219,16 @@ void BufferTextureGLTest::setBufferOffset() {
     };
     buffer.setData({nullptr, 1024}, BufferUsage::StaticDraw);
     buffer.setSubData(256 - 16, data);
-    texture.setBuffer(BufferTextureFormat::R8UI, buffer, 256, 8);
+    texture.setBuffer(BufferTextureFormat::RGBA8UI, buffer, 256, 8);
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
+    #ifdef MAGNUM_TARGET_GLES
+    if(!Context::current().isVersionSupported(Version::GLES310))
+        CORRADE_SKIP("OpenGL ES 3.1 not supported, skipping image size testing.");
+    #endif
+
+    CORRADE_COMPARE(texture.size(), 2);
 
     MAGNUM_VERIFY_NO_GL_ERROR();
 }