Added NoCreate {Compressed,}BufferImage constructors.

To have common API across the board.

src/Magnum/BufferImage.cpp

@@ -25,6 +25,8 @@
 
 #include "BufferImage.h"
 
+#include "Magnum/PixelFormat.h"
+
 namespace Magnum {
 
 #ifndef MAGNUM_TARGET_GLES2
@@ -39,6 +41,8 @@ template<UnsignedInt dimensions> BufferImage<dimensions>::BufferImage(const Pixe
 
 template<UnsignedInt dimensions> BufferImage<dimensions>::BufferImage(const PixelStorage storage, const PixelFormat format, const PixelType type): _storage{storage}, _format{format}, _type{type}, _buffer{Buffer::TargetHint::PixelPack}, _dataSize{0} {}
 
+template<UnsignedInt dimensions> BufferImage<dimensions>::BufferImage(NoCreateT) noexcept: _format{PixelFormat::RGBA}, _type{PixelType::UnsignedByte}, _buffer{NoCreate}, _dataSize{} {}
+
 template<UnsignedInt dimensions> void BufferImage<dimensions>::setData(const PixelStorage storage, const PixelFormat format, const PixelType type, const VectorTypeFor<dimensions, Int>& size, Containers::ArrayView<const void> const data, const BufferUsage usage) {
     _storage = storage;
     _format = format;
@@ -88,6 +92,8 @@ template<UnsignedInt dimensions> CompressedBufferImage<dimensions>::CompressedBu
     #endif
     _format{}, _buffer{Buffer::TargetHint::PixelPack}, _dataSize{} {}
 
+template<UnsignedInt dimensions> CompressedBufferImage<dimensions>::CompressedBufferImage(NoCreateT) noexcept: _format{}, _buffer{NoCreate}, _dataSize{} {}
+
 template<UnsignedInt dimensions> void CompressedBufferImage<dimensions>::setData(
     #ifndef MAGNUM_TARGET_GLES
     const CompressedPixelStorage storage,

src/Magnum/BufferImage.h

@@ -128,6 +128,17 @@ template<UnsignedInt dimensions> class BufferImage {
          */
         /*implicit*/ BufferImage(PixelFormat format, PixelType type): BufferImage{{}, format, type} {}
 
+        /**
+         * @brief Construct without creating the underlying OpenGL object
+         *
+         * The constructed instance is equivalent to moved-from state with
+         * @ref PixelFormat::RGBA and @ref PixelType::UnsignedByte. Useful in
+         * cases where you will overwrite the instance later anyway. Move
+         * another object over it to make it useful.
+         * @see @ref BufferImage(), @ref wrap()
+         */
+        explicit BufferImage(NoCreateT) noexcept;
+
         /** @brief Copying is not allowed */
         BufferImage(const BufferImage<dimensions>&) = delete;
 
@@ -348,6 +359,16 @@ template<UnsignedInt dimensions> class CompressedBufferImage {
          */
         /*implicit*/ CompressedBufferImage();
 
+        /**
+         * @brief Construct without creating the underlying OpenGL object
+         *
+         * The constructed instance is equivalent to moved-from state. Useful
+         * in cases where you will overwrite the instance later anyway. Move
+         * another object over it to make it useful.
+         * @see @ref BufferImage(), @ref wrap()
+         */
+        explicit CompressedBufferImage(NoCreateT) noexcept;
+
         /** @brief Copying is not allowed */
         CompressedBufferImage(const CompressedBufferImage<dimensions>&) = delete;
 

src/Magnum/Test/BufferImageGLTest.cpp

@@ -36,6 +36,8 @@ struct BufferImageGLTest: OpenGLTester {
 
     void construct();
     void constructCompressed();
+    void constructNoCreate();
+    void constructNoCreateCompressed();
     void constructBuffer();
     void constructBufferCompressed();
     void constructCopy();
@@ -53,6 +55,8 @@ struct BufferImageGLTest: OpenGLTester {
 BufferImageGLTest::BufferImageGLTest() {
     addTests({&BufferImageGLTest::construct,
               &BufferImageGLTest::constructCompressed,
+              &BufferImageGLTest::constructNoCreate,
+              &BufferImageGLTest::constructNoCreateCompressed,
               &BufferImageGLTest::constructBuffer,
               &BufferImageGLTest::constructBufferCompressed,
               &BufferImageGLTest::constructCopy,
@@ -119,6 +123,28 @@ void BufferImageGLTest::constructCompressed() {
     #endif
 }
 
+void BufferImageGLTest::constructNoCreate() {
+    {
+        BufferImage2D image{NoCreate};
+
+        MAGNUM_VERIFY_NO_ERROR();
+        CORRADE_COMPARE(image.buffer().id(), 0);
+    }
+
+    MAGNUM_VERIFY_NO_ERROR();
+}
+
+void BufferImageGLTest::constructNoCreateCompressed() {
+    {
+        CompressedBufferImage2D image{NoCreate};
+
+        MAGNUM_VERIFY_NO_ERROR();
+        CORRADE_COMPARE(image.buffer().id(), 0);
+    }
+
+    MAGNUM_VERIFY_NO_ERROR();
+}
+
 void BufferImageGLTest::constructBuffer() {
     const char data[] = { 'a', 'b', 'c' };
     Buffer buffer;