More intuitive framebuffer attachment mapping.

src/DefaultFramebuffer.cpp

@@ -27,15 +27,27 @@ DefaultFramebuffer defaultFramebuffer;
 DefaultFramebuffer::DefaultFramebuffer() { _id = 0; }
 
 #ifndef MAGNUM_TARGET_GLES2
-void DefaultFramebuffer::mapForDraw(std::initializer_list<DrawAttachment> attachments) {
-    GLenum* _attachments = new GLenum[attachments.size()];
-    for(auto it = attachments.begin(); it != attachments.end(); ++it)
-        _attachments[it-attachments.begin()] = static_cast<GLenum>(*it);
+void DefaultFramebuffer::mapForDraw(std::initializer_list<std::pair<GLuint, DrawAttachment>> attachments) {
+    /* Max attachment location */
+    std::size_t max = 0;
+    for(const auto& attachment: attachments)
+        if(attachment.first > max) max = attachment.first;
+
+    /* Create linear array from associative */
+    GLenum* _attachments = new GLenum[max+1];
+    std::fill_n(_attachments, max, GL_NONE);
+    for(const auto& attachment: attachments)
+        _attachments[attachment.first] = static_cast<GLenum>(attachment.second);
 
     bindInternal(drawTarget);
-    glDrawBuffers(attachments.size(), _attachments);
+    glDrawBuffers(max+1, _attachments);
     delete[] _attachments;
 }
+
+void DefaultFramebuffer::mapForDraw(DrawAttachment attachment) {
+    bindInternal(drawTarget);
+    glDrawBuffer(static_cast<GLenum>(attachment));
+}
 #endif
 
 void DefaultFramebuffer::mapForRead(ReadAttachment attachment) {

src/DefaultFramebuffer.h

@@ -168,21 +168,38 @@ class MAGNUM_EXPORT DefaultFramebuffer: public AbstractFramebuffer {
 
         #ifndef MAGNUM_TARGET_GLES2
         /**
-         * @brief Map given attachments for drawing
-         * @param attachments       Attachments. If any value is
-         *      @ref DrawAttachment "Attachment::None", given output is not
-         *      used.
+         * @brief Map shader outputs to buffer attachment
          *
+         * @p attachments is list of shader outputs mapped to framebuffer
+         * buffer attachments. Shader outputs which are not listed are not
+         * used, you can achieve the same by passing @ref DrawAttachment "DrawAttachment::None"
+         * as attachment. Example usage:
+         * @code
+         * framebuffer.mapForDraw({{MyShader::ColorOutput, DefaultFramebuffer::DrawAttachment::BackLeft},
+         *                         {MyShader::NormalOutput, DefaultFramebuffer::DrawAttachment::None}});
+         * @endcode
          * @see mapForRead(), @fn_gl{BindFramebuffer}, @fn_gl{DrawBuffers}
          * @requires_gles30 Draw attachments for default framebuffer are
          *      available only in OpenGL ES 3.0.
          */
-        void mapForDraw(std::initializer_list<DrawAttachment> attachments);
+        void mapForDraw(std::initializer_list<std::pair<GLuint, DrawAttachment>> attachments);
+
+        /**
+         * @brief Map shader output to buffer attachment
+         * @param attachment        Buffer attachment
+         *
+         * Similar to above function, can be used in cases when shader has
+         * only one (unnamed) output.
+         * @see mapForRead(), @fn_gl{BindFramebuffer}, @fn_gl{DrawBuffer}
+         * @requires_gles30 Draw attachments for default framebuffer are
+         *      available only in OpenGL ES 3.0.
+         */
+        void mapForDraw(DrawAttachment attachment);
         #endif
 
         /**
          * @brief Map given attachment for reading
-         * @param attachment        Attachment
+         * @param attachment        Buffer attachment
          *
          * @see mapForDraw(), @fn_gl{BindFramebuffer}, @fn_gl{ReadBuffer}
          * @requires_gles30 %Extension @es_extension2{NV,read_buffer,GL_NV_read_buffer}

src/Framebuffer.cpp

@@ -42,17 +42,29 @@ Framebuffer::~Framebuffer() {
     glDeleteFramebuffers(1, &_id);
 }
 
-void Framebuffer::mapForDraw(std::initializer_list<std::int8_t> colorAttachments) {
-    GLenum* attachments = new GLenum[colorAttachments.size()];
-    for(auto it = colorAttachments.begin(); it != colorAttachments.end(); ++it)
-        attachments[it-colorAttachments.begin()] = *it + GL_COLOR_ATTACHMENT0;
-
-    bindInternal(Target::Draw);
+void Framebuffer::mapForDraw(std::initializer_list<std::pair<GLuint, std::int8_t>> attachments) {
+    /* Max attachment location */
+    std::size_t max = 0;
+    for(const auto& attachment: attachments)
+        if(attachment.first > max) max = attachment.first;
+
+    /* Create linear array from associative */
+    GLenum* _attachments = new GLenum[max+1];
+    std::fill_n(_attachments, max, GL_NONE);
+    for(const auto& attachment: attachments)
+        _attachments[attachment.first] = attachment.second < 0 ? GL_NONE : GL_COLOR_ATTACHMENT0 + attachment.second;
+
+    bindInternal(drawTarget);
     /** @todo Re-enable when extension wrangler is available for ES2 */
     #ifndef MAGNUM_TARGET_GLES2
-    glDrawBuffers(colorAttachments.size(), attachments);
+    glDrawBuffers(max+1, _attachments);
     #endif
-    delete[] attachments;
+    delete[] _attachments;
+}
+
+void Framebuffer::mapForDraw(std::int8_t attachment) {
+    bindInternal(drawTarget);
+    glDrawBuffer(static_cast<GLenum>(attachment));
 }
 
 void Framebuffer::mapForRead(std::uint8_t colorAttachment) {

src/Framebuffer.h

@@ -49,23 +49,40 @@ class MAGNUM_EXPORT Framebuffer: public AbstractFramebuffer {
         ~Framebuffer();
 
         /**
-         * @brief Map given color attachments of current framebuffer for drawing
-         * @param colorAttachments  Color attachment IDs. If any value is -1,
-         *      given output is not used.
+         * @brief Map shader output to color attachment
          *
+         * @p attachments is list of shader outputs mapped to framebuffer
+         * color attachment IDs. Shader outputs which are not listed are not
+         * used, you can achieve the same by passing `-1` as color attachment
+         * ID. Example usage:
+         * @code
+         * framebuffer.mapForDraw({{MyShader::ColorOutput, 0},
+         *                         {MyShader::NormalOutput, 1}});
+         * @endcode
          * @see mapForRead(), @fn_gl{BindFramebuffer}, @fn_gl{DrawBuffers}
          * @requires_gles30 %Extension @es_extension2{NV,draw_buffers,GL_NV_draw_buffers}
          */
-        void mapForDraw(std::initializer_list<std::int8_t> colorAttachments);
+        void mapForDraw(std::initializer_list<std::pair<GLuint, std::int8_t>> attachments);
 
         /**
-         * @brief Map given color attachment of current framebuffer for reading
-         * @param colorAttachment   Color attachment ID
+         * @brief Map shader output to color attachment
+         * @param attachment        Color attachment ID
+         *
+         * Similar to above function, can be used in cases when shader has
+         * only one (unnamed) output.
+         * @see mapForRead(), @fn_gl{BindFramebuffer}, @fn_gl{DrawBuffer}
+         * @requires_gles30 %Extension @es_extension2{NV,draw_buffers,GL_NV_draw_buffers}
+         */
+        void mapForDraw(std::int8_t attachment);
+
+        /**
+         * @brief Map given color attachment for reading
+         * @param attachment        Color attachment ID
          *
          * @see mapForDraw(), @fn_gl{BindFramebuffer}, @fn_gl{ReadBuffer}
          * @requires_gles30 %Extension @es_extension2{NV,read_buffer,GL_NV_read_buffer}
          */
-        void mapForRead(std::uint8_t colorAttachment);
+        void mapForRead(std::uint8_t attachment);
 
         /**
          * @brief Attachment for depth/stencil part of fragment shader output