Name IMG_multisampled_render_to_texture Name Strings GL_IMG_multisampled_render_to_texture Contact Georg Kolling, Imagination Technologies (georg.kolling 'at' imgtec.com) Status Complete Version Last Modified Date: March 26, 2010 Revision: 3 Number OpenGL ES Extension #74 Dependencies OpenGL ES 2.0 or OES_framebuffer_object are required. This extension is written against the OpenGL ES 2.0 Specification. Overview This extension introduces functionality to perform multisampled rendering to a color renderable texture, without requiring an explicit resolve of multisample data. Some GPU architectures - such as tile-based renderers - are capable of performing multisampled rendering by storing multisample data in internal high-speed memory and downsampling the data when writing out to external memory after rendering has finished. Since per-sample data is never written out to external memory, this approach saves bandwidth and storage space. In this case multisample data gets discarded, however this is acceptable in most cases. The extension provides a new command, FramebufferTexture2DMultisampleIMG, which attaches a texture level to a framebuffer and enables multisampled rendering to that texture level. When the texture level is used as a source or destination for any operation other than drawing to it, an implicit resolve of multisampled color data is performed. After such a resolve, the multisampled color data is discarded. In order to allow the use of multisampled depth and stencil buffers when performing multisampled rendering to a texture, the extension also adds the command RenderbufferStorageMultisampleIMG. IP Status No known IP claims. New Procedures and Functions void RenderbufferStorageMultisampleIMG( enum target, sizei samples, enum internalformat, sizei width, sizei height); void FramebufferTexture2DMultisampleIMG( enum target, enum attachment, enum textarget, uint texture, int level, sizei samples); New Tokens Accepted by the parameter of GetRenderbufferParameteriv: RENDERBUFFER_SAMPLES_IMG 0x9133 Returned by CheckFramebufferStatus: FRAMEBUFFER_INCOMPLETE_MULTISAMPLE_IMG 0x9134 Accepted by the parameter of GetBooleanv, GetIntegerv, GetFloatv, and GetDoublev: MAX_SAMPLES_IMG 0x9135 Accepted by the parameter of GetFramebufferAttachmentParameteriv: TEXTURE_SAMPLES_IMG 0x9136 Additions to Section 4.4.3 of the OpenGL ES 2.0 Specification (Renderbuffer Objects) Replace the paragraph describing the command RenderbufferStorage with the following: The command void RenderbufferStorageMultisampleIMG( enum target, sizei samples, enum internalformat, sizei width, sizei height ); establishes the data storage, format, dimensions, and number of samples of a renderbuffer object's image. target must be RENDERBUFFER. internalformat must be one of the color-renderable, depth-renderable, or stencil-renderable formats described in table 4.5. width and height are the dimensions in pixels of the renderbuffer. If either width or height is greater than the value of MAX_RENDERBUFFER_SIZE, or if samples is greater than the value of MAX_SAMPLES_IMG, then the error INVALID_VALUE is generated. If OpenGL ES is unable to create a data store of the requested size, the error OUT_OF_MEMORY is generated. Upon success, RenderbufferStorageMultisampleIMG deletes any existing data store for the renderbuffer image and the contents of the data store after calling RenderbufferStorageMultisampleIMG are undefined. RENDERBUFFER_WIDTH is set to width, RENDERBUFFER_HEIGHT is set to height, and RENDERBUFFER_INTERNAL_FORMAT is set to internalformat. If samples is zero, then RENDERBUFFER_SAMPLES_IMG is set to zero. Otherwise samples represents a request for a desired minimum number of samples. Since different implementations may support different sample counts for multisampled rendering, the actual number of samples allocated for the renderbuffer image is implementation-dependent. However, the resulting value for RENDERBUFFER_SAMPLES_IMG is guaranteed to be greater than or equal to samples and no more than the next larger sample count supported by the implementation. An OpenGL ES implementation may vary its allocation of internal component resolution based on any RenderbufferStorageMultisampleIMG parameter (except target), but the allocation and chosen internal format must not be a function of any other state and cannot be changed once they are established. The command void RenderbufferStorage( enum target, enum internalformat, sizei width, sizei height ); is equivalent to calling RenderbufferStorageMultisampleIMG with samples equal to zero. Add the following after the paragraph describing FramebufferTexture2D: The command void FramebufferTexture2DMultisampleIMG( enum target, enum attachment, enum textarget, uint texture, int level, sizei samples ); enables multisampled rendering into the images of a texture object. target, textarget, texture, and level correspond to the same parameters for FramebufferTexture2D and have the same restrictions. attachment must be COLOR_ATTACHMENT0. If samples is greater than the value of MAX_SAMPLES_IMG, then the error INVALID_VALUE is generated. If samples is zero, then TEXTURE_SAMPLES_IMG is set to zero, and FramebufferTexture2DMultisampleIMG behaves like FramebufferTexture2D. Otherwise samples represents a request for a desired minimum number of samples. Since different implementations may support different sample counts for multisampled rendering, the actual number of samples allocated for the image is implementation-dependent. However, the resulting value for TEXTURE_SAMPLES_IMG is guaranteed to be greater than or equal to samples and no more than the next larger sample count supported by the implementation. The implementation allocates an implicit multisample buffer with TEXTURE_SAMPLES_IMG samples and the same internalformat, width, and height as the specified texture level. This buffer is used as the target for rendering instead of the specified texture level. The buffer is associated with the attachment and gets deleted after the attachment is broken. When the texture level is used as a source or destination for any operation, or when the attachment is broken, an implicit resolve of multisample data from the multisample buffer to the texture level is performed. After such a resolve, the contents of the multisample buffer become undefined. The operations which cause a resolve include: - Drawing with the texture bound to an active texture unit - ReadPixels or CopyTex[Sub]Image* while the texture is attached to the framebuffer - CopyTex[Sub]Image*, Tex[Sub]Image*, CompressedTex[Sub]Image* with the specified level as destination - GenerateMipmap Additions to section 4.4.5 of the OpenGL ES 2.0 Specification (Framebuffer Completeness) Add the following bullet point after * All attached images have the same width and height. FRAMEBUFFER_INCOMPLETE_DIMENSIONS on page 116: * The value of RENDERBUFFER_SAMPLES_IMG is the same for all attached renderbuffers; the value of TEXTURE_SAMPLES_IMG is the same for all texture attachments; and, if the attached images are a mix of renderbuffers and textures, the value of RENDERBUFFER_SAMPLES_IMG matches the value of TEXTURE_- SAMPLES_IMG. FRAMEBUFFER_INCOMPLETE_MULTISAMPLE Dependencies on GL and ES profiles, versions, and other extensions None Errors The error OUT_OF_MEMORY is generated when RenderbufferStorageMultisampleIMG cannot create storage of the specified size. If RenderbufferStorageMultisampleEXT is called with a value of that is greater than MAX_SAMPLES_IMG, then the error INVALID_VALUE is generated. The error INVALID_ENUM is generated if FramebufferTexture2DMultisampleIMG is called with a that is not FRAMEBUFFER. The error INVALID_ENUM is generated if FramebufferTexture2DMultisampleIMG is called with an that is not COLOR_ATTACHMENT0. The error INVALID_ENUM is generated if FramebufferTexture2DMultisampleIMG is called with a that is not TEXTURE_2D, TEXTURE_CUBE_MAP_POSITIVE_X, TEXTURE_CUBE_MAP_POSITIVE_Y, TEXTURE_CUBE_MAP_POSITIVE_Z, TEXTURE_CUBE_MAP_NEGATIVE_X, TEXTURE_CUBE_MAP_NEGATIVE_Y, or TEXTURE_CUBE_MAP_NEGATIVE_Z. New State Changes to table 6.22, p. 154 (Renderbuffer State) Initial Get Value Type Get Command Value Description Sec. --------- ---- ---------------- ------- ------------ ----- RENDERBUFFER_SAMPLES_IMG Z+ GetRenderbuffer- 0 Renderbuffer 4.4.3 Parameteriv samples Changes to table 6.23, p. 155 (Framebuffer State) Initial Get Value Type Get Command Value Description Sec. --------- ------ --------------------- ------- --------------- ---- TEXTURE_SAMPLES_IMG n * Z+ GetFramebuffer- 0 Framebuffer 4.4 AttachmentParameteriv texture samples New Implementation Dependent State Changes to table 6.17, p. 149 (Implementation Dependent Values) Minimum Get Value Type Get Command Value Description Sec. --------- ---- ----------- ------- ----------- ---- MAX_SAMPLES_IMG Z+ GetIntegerv 2 Max. # of 4.4 samples. Sample Code GLsizei width = ...; GLsizei height = ...; GLint samples; glGetIntegerv(GL_MAX_SAMPLES_IMG, &samples); /* Create multisampled depth renderbuffer */ GLuint depthbuffer; glGenRenderbuffers(1, &depthbuffer); glBindRenderbuffer(GL_RENDERBUFFER, depthbuffer); glRenderbufferStorageMultisampleIMG(GL_RENDERBUFFER, samples, GL_DEPTH_COMPONENT16, width, height); glBindRenderbuffer(GL_RENDERBUFFER, 0); /* Create RGBA texture with single mipmap level */ GLuint texture; glGenTextures(1, &texture); glBindTexture(GL_TEXTURE_2D, texture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4, NULL); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glBindTexture(GL_TEXTURE_2D, 0); /* Create framebuffer object, attach texture and depth renderbuffer */ GLuint framebuffer; glGenFramebuffers(1, &framebuffer); glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthbuffer); glFramebufferTexture2DMultisampleIMG(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0, samples); /* handle unsupported cases */ if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) { ... } /* draw to the texture */ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); ... /* Discard the depth renderbuffer contents if possible */ if (extension_supported("GL_EXT_discard_framebuffer")) { GLenum discard_attachments[] = { GL_DEPTH_EXT }; glDiscardFramebufferEXT(GL_FRAMEBUFFER, 1, discard_attachments); } /* Draw to the default framebuffer using the antialiased texture */ /* Color data is implicitly resolved before the texture gets used */ glBindFramebuffer(GL_FRAMEBUFFER, 0); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT); glBindTexture(GL_TEXTURE_2D, texture); ... Conformance Tests No conformance test has been defined yet Issues Revision History Revision 3, 2010/03/26 - Set enums to undefined Revision 2, 2010/03/24 - Removed error condition for glReadPixels and glCopyTexImage2D Revision 1, 2010/01/05 - First draft of extension