| Name |
| |
| EXT_multiview_draw_buffers |
| |
| Name Strings |
| |
| GL_EXT_multiview_draw_buffers |
| |
| Contributors |
| |
| Acorn Pooley, NVIDIA |
| Greg Roth, NVIDIA |
| Maurice Ribble, Qualcomm |
| |
| Contact |
| |
| Greg Roth (groth 'at' nvidia.com) |
| |
| Version |
| |
| Version 3, Sept 03, 2011 |
| |
| Number |
| |
| OpenGL ES Extension #125 |
| |
| Status |
| |
| Complete |
| |
| Dependencies |
| |
| Written against the OpenGL ES 2.0 Specification |
| |
| NV_draw_buffers affects the definition of this extension. |
| |
| OpenGL ES 3.0 affects the definition of this extension. |
| |
| Overview |
| |
| This extension allows selecting among draw buffers as the |
| rendering target. This may be among multiple primary buffers |
| pertaining to platform-specific stereoscopic or multiview displays |
| or among offscreen framebuffer object color attachments. |
| |
| To remove any artificial limitations imposed on the number of |
| possible buffers, draw buffers are identified not as individual |
| enums, but as pairs of values consisting of an enum representing |
| buffer locations such as COLOR_ATTACHMENT_EXT or MULTIVIEW_EXT, |
| and an integer representing an identifying index of buffers of this |
| location. These (location, index) pairs are used to specify draw |
| buffer targets using a new DrawBuffersIndexedEXT call. |
| |
| Rendering to buffers of location MULTIVIEW_EXT associated with the |
| context allows rendering to multiview buffers created by EGL using |
| EGL_EXT_multiview_window for stereoscopic displays. |
| |
| Rendering to COLOR_ATTACHMENT_EXT buffers allows implementations to |
| increase the number of potential color attachments indefinitely to |
| renderbuffers and textures. |
| |
| This extension allows the traditional quad buffer stereoscopic |
| rendering method that has proven effective by indicating a left or |
| right draw buffer and rendering to each accordingly, but is also |
| dynamic enough to handle an arbitrary number of color buffer targets |
| all using the same shader. This grants the user maximum flexibility |
| as well as a familiar interface. |
| |
| New Procedures and Functions |
| |
| void ReadBufferIndexedEXT(enum src, int index); |
| void DrawBuffersIndexedEXT(int n, const enum *location, |
| const int *indices); |
| void GetIntegeri_vEXT(enum target, uint index, int *data); |
| |
| New Tokens |
| |
| Accepted by the <location> parameter of DrawBuffersIndexedEXT: |
| |
| COLOR_ATTACHMENT_EXT 0x90F0 |
| MULTIVIEW_EXT 0x90F1 |
| |
| Accepted by the <target> parameter of GetIntegeri_EXT: |
| |
| DRAW_BUFFER_EXT 0x0C01 |
| READ_BUFFER_EXT 0x0C02 |
| |
| Accepted by the <target> parameter of GetInteger: |
| |
| MAX_MULTIVIEW_BUFFERS_EXT 0x90F2 |
| |
| |
| Changes to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment |
| Operations and the Frame Buffer) |
| |
| Modify section 4.2.1, "Selecting a Buffer for Writing" |
| |
| Change first paragraph to: |
| |
| By default, color values are written into the front buffer for |
| single buffered contexts or into the back buffer for back buffered |
| contexts as determined when creating the GL context. To control |
| the color buffer into which each of the fragment color values is |
| written, DrawBuffersNV or DrawBuffersIndexedEXT is used. |
| |
| Add to the end of 4.2.1: |
| |
| The command |
| |
| void DrawBuffersIndexedEXT(sizei n, const enum *locations, |
| const int *indices); |
| |
| defines the draw buffers to which all fragment colors are written. |
| <n> specifies the number of values in <locations> and <indices>. |
| <locations> is a pointer to an array of symbolic constants |
| specifying the location of the draw buffer. <indices> is a pointer |
| to an array of integer values specifying the index of the draw |
| buffer. Together <locations> and <indices> specify the draw buffer |
| to which each fragment color is written. |
| |
| Each constant in <locations> must be MULTIVIEW_EXT, COLOR_- |
| ATTACHMENT_EXT, or NONE. Otherwise, an INVALID_ENUM error is |
| generated. Further, acceptable values for the constants in |
| <locations> depend on whether the GL is using the default |
| framebuffer (i.e. DRAW_FRAMEBUFFER_BINDING is non-zero). For more |
| information about framebuffer objects, see section 4.4. |
| |
| If the GL is bound to the default framebuffer, then each of the |
| location constants must be MULTIVIEW_EXT or NONE. |
| |
| If the GL is bound to a framebuffer object, then each of the |
| location constants must be COLOR_ATTACHMENT_EXT or NONE. |
| |
| Where the constant in <locations> is MULTIVIEW_EXT, the |
| corresponding value in <indices> must be a value from 0 through |
| MAX_MULTIVIEW_BUFFERS_EXT. Where the constant in <locations> is |
| COLOR_ATTACHMENT_EXT, the value in <indices> must be a value from 0 |
| through MAX_COLOR_ATTACHMENTS_NV. Otherwise, an INVALID_OPERATION |
| error is generated. Where the constant in <locations> is NONE, the |
| value in <indices> is ignored. |
| |
| For monoscopic rendering, the only available view is index 0. For |
| stereoscopic rendering, view index 0 corresponds to the left buffer |
| and view index 1 corresponds to the right buffer. |
| |
| The draw buffers being defined correspond, in order, to the |
| respective fragment colors. The draw buffer for fragment colors |
| beyond <n> is set to NONE. |
| |
| Except for where the constant in <locations> is NONE, a buffer may |
| not be specified more than once by the arrays pointed to by |
| <locations> and <indices>. Specifying a buffer more than once will |
| result in the error INVALID_OPERATION. |
| |
| If a fragment shader writes to "gl_FragColor", DrawBuffersIndexedEXT |
| specifies a set of draw buffers into which the color written to |
| "gl_FragColor" is written. If a fragment shader writes to |
| gl_FragData, DrawBuffersIndexedEXT specifies a set of draw buffers |
| into which each of the multiple output colors defined by these |
| variables are separately written. If a fragment shader writes to |
| neither gl_FragColor nor gl_FragData, the values of the fragment |
| colors following shader execution are undefined, and may differ |
| for each fragment color. |
| |
| Indicating a buffer or buffers using DrawBuffersIndexedEXT causes |
| subsequent pixel color value writes to affect the indicated |
| buffers. If more than one color buffer is selected for drawing, |
| blending is computed and applied independently for each buffer. |
| |
| Specifying NONE in the <locations> array for a fragment color will |
| inhibit that fragment color from being written to any buffer. |
| |
| Monoscopic surfaces include only left buffers, while stereoscopic |
| surfaces include a left and a right buffer, and multiview surfaces |
| include more than 1 buffer (a stereoscopic surface is a multiview |
| surface with 2 buffers). The type of surface is selected at EGL |
| surface initialization. |
| |
| The state required to handle color buffer selection is two integers |
| for each supported fragment color for each framebuffer or |
| framebuffer object. For the default framebuffer, the initial state |
| of the draw buffer location for fragment color zero is MULTIVIEW_EXT |
| and the index is 0. For framebuffer objects, the initial state of |
| the draw buffer location for fragment color zero is COLOR_- |
| ATTACHMENT_EXT and the index is 0. The initial state of draw buffers |
| for fragment colors other than zero is NONE. |
| |
| The color buffer location and index to which fragment colors are |
| written for an output color index <i> can be queried by calling |
| GetIntegeri_vEXT with <target> DRAW_BUFFER_EXT and index |
| <i>. This returns a pair of values representing the draw buffer |
| location and index. The number of multiview buffers available to a |
| GL context can be queried by calling GetIntegerv with <target> |
| MAX_MULTIVIEW_BUFFERS_EXT. |
| |
| Section 4.3.1 (Reading Pixels), subsection "Obtaining Pixels from |
| the Framebuffer" add: |
| |
| For color formats, the read buffer from which values are obtained is |
| one of the color buffers; the selection of color buffer is |
| controlled with ReadBufferIndexedEXT. |
| |
| The command |
| |
| void ReadBufferIndexedEXT(enum location, int index); |
| |
| takes a symbolic constant and integer pair to select the color |
| buffer from which color values are obtained. <location> must be one |
| of MULTIVIEW_EXT, COLOR_ATTACHMENT_EXT, or NONE. Otherwise, an |
| INVALID_ENUM error is generated. If <location> is MULTIVIEW_EXT, |
| <index> must be a value from 0 through MAX_MULTIVIEW_BUFFERS_EXT. |
| If <location> is COLOR_ATTACHMENT_EXT, <index> must be a value from |
| 0 through MAX_COLOR_ATTACHMENTS_NV. Otherwise, an INVALID_OPERATION |
| error is generated. If <location> is NONE, <index> is ignored. |
| |
| The acceptable values for <location> depend on whether the GL is |
| using the default framebuffer (i.e. FRAMEBUFFER_BINDING is zero), or |
| a framebuffer object (i.e. FRAMEBUFFER_BINDING is non-zero). For |
| more information about framebuffer objects, see section 4.4. |
| |
| If the object bound to FRAMEBUFFER_BINDING is not framebuffer |
| complete (as defined in section 4.4.5), then ReadPixels generates |
| the error INVALID_FRAMEBUFFER_OPERATION. If <location> is a constant |
| that is neither legal for the default framebuffer, nor legal for a |
| framebuffer object, then the error INVALID_ENUM results. |
| |
| When FRAMEBUFFER_BINDING is zero, i.e. the default framebuffer, |
| <location> must be MULTIVIEW_EXT or NONE. If the buffer indicated by |
| <index> is missing, the error INVALID_OPERATION is generated. For |
| the default framebuffer, the initial setting for READ_BUFFER_EXT is |
| <location> of MULTIVIEW_EXT and <index> of zero. |
| |
| When the GL is using a framebuffer object, <location> must be NONE |
| or COLOR_ATTACHMENT_EXT. Specifying COLOR_ATTACHMENT_EXT enables |
| reading from the image attached to the framebuffer at COLOR_- |
| ATTACHMENT<index>_NV. For framebuffer objects, the initial setting |
| for READ_BUFFER_EXT is <location> of COLOR_ATTACHMENT_EXT and |
| <index> of zero. |
| |
| ReadPixels generates an INVALID_OPERATION error if it attempts to |
| select a color buffer while READ_BUFFER_EXT is none. |
| |
| Changes to chapter 6 |
| |
| Add to section 6.1.1, "Simple Queries" before description of |
| IsEnabled: |
| |
| Indexed simple state variables are queried with the command |
| |
| void GetIntegeri_vEXT(enum target, uint index, int* data); |
| |
| <target> is the name of the indexed state and <index> is the |
| index of the particular element being queried. <data> is a |
| pointer to a scalar or array of the indicated type in which |
| to place the returned data. An INVALID_VALUE error is generated |
| if <index> is outside the valid range for the indexed state |
| <target>. |
| |
| Changes to Chapter 3 of the OpenGL Shading Language 1.0 Specification |
| (Basics) |
| |
| Add a new section: |
| |
| 3.4.1 GL_EXT_multiview_draw_buffers Extension |
| |
| To use the GL_EXT_multiview_draw_buffers extension in a shader it |
| must be enabled using the #extension directive. |
| |
| The shading language preprocessor #define GL_EXT_multiview_draw_- |
| buffers will be defined to 1, if the GL_EXT_multiview_draw_buffers |
| extension is supported. |
| |
| Dependencies on NV_draw_buffers: |
| |
| If NV_draw_buffers is not supported and OpenGL ES 3 is, add to the |
| description of DrawBuffersIndexedEXT: |
| |
| The <i>th index listed in <indices> must be <i> or NONE. |
| Specifying a buffer out of order will generate the error |
| INVALID_OPERATION. |
| |
| If neither NV_draw_buffers nor OpenGL ES 3 is supported, all |
| references to DrawBuffersNV and color attachments are removed. The |
| following is substituted for the above changes to Chapter 4 (Per- |
| Fragment Operations and the Frame Buffer): |
| |
| Change section 4.2.1, "Selecting a Buffer for Writing" |
| |
| Change first paragraph to: |
| |
| By default, color values are written into the front buffer for |
| single buffered contexts or into the back buffer for back buffered |
| contexts as determined when creating the GL context. To control |
| the color buffer into which each of the fragment color values is |
| written, DrawBuffersIndexedEXT is used. |
| |
| Add to the end of 4.2.1: |
| |
| The command |
| |
| void DrawBuffersIndexedEXT(sizei n, const enum *locations, |
| const int *indices); |
| |
| defines the draw buffers to which all fragment colors are written. |
| <n> specifies the number of values in <locations> and <indices>. |
| <locations> is a pointer to an array of symbolic constants |
| specifying the location of the draw buffer. <indices> is a pointer |
| to an array of integer values specifying the index of the draw |
| buffer. Together <locations> and <indices> specify the draw buffer |
| to which each fragment color is written. |
| |
| Each constant in <locations> must be MULTIVIEW_EXT or NONE. |
| Otherwise, an INVALID_ENUM error is generated. |
| |
| DrawBuffersIndexedEXT generates an INVALID_OPERATION error if the GL |
| is bound to a framebuffer object. |
| |
| Where the constant in <locations> is MULTIVIEW_EXT, the |
| corresponding value in <indices> must be a value from 0 through |
| MAX_MULTIVIEW_BUFFERS_EXT. Otherwise, an INVALID_OPERATION error is |
| generated. Where the constant in <locations> is NONE, the value |
| in <indices> is ignored. |
| |
| An INVALID_VALUE error is generated if <n> is not 1. |
| |
| For monoscopic rendering, the only available view is index 0. For |
| stereoscopic rendering, view index 0 is left and view index 1 is |
| right. |
| |
| If a fragment shader writes to "gl_FragColor" or "gl_FragData[0]", |
| DrawBuffersIndexedEXT specifies a set of draw buffers into which the |
| output color is written. If a fragment shader writes to neither |
| gl_FragColor nor gl_FragData[0], the values of the fragment colors |
| following shader execution are undefined, and may differ for each |
| fragment color. |
| |
| Indicating a buffer using DrawBuffersIndexedEXT causes subsequent |
| pixel color value writes to affect the indicated buffer. |
| |
| Specifying NONE in the <locations> array for a fragment color will |
| inhibit that fragment color from being written to any buffer. |
| |
| Monoscopic surfaces include only left buffers, while stereoscopic |
| surfaces include a left and a right buffer, and multiview surfaces |
| include more than 1 buffer (a stereoscopic surface is a multiview |
| surface with 2 buffers). The type of surface is selected at EGL |
| surface initialization. |
| |
| The state required to handle color buffer selection is two integers |
| for the fragment color output for each framebuffer or framebuffer |
| object. For the default framebuffer, the initial state of the draw |
| buffer location for fragment color zero is MULTIVIEW_EXT and the |
| index is 0. For framebuffer objects, the initial state of the draw |
| buffer location for fragment color zero is COLOR_ATTACHMENT_EXT and |
| the index is 0. |
| |
| The color buffer location and index to which fragment colors are |
| written can be queried by calling GetIntegeri_vEXT with <target> |
| DRAW_BUFFER_EXT and index 0. This returns a pair of values |
| representing the draw buffer location and index. The number of |
| multiview buffers available to a GL context can be queried by |
| calling GetIntegerv with <target> MAX_MULTIVIEW_BUFFERS_EXT. |
| |
| The command |
| |
| void ReadBufferIndexedEXT(enum location, int index); |
| |
| takes a symbolic constant and integer pair to select the color |
| buffer from which color values are obtained. <location> must be |
| MULTIVIEW_EXT or NONE. Otherwise, an INVALID_ENUM error is |
| generated. If <location> is MULTIVIEW_EXT, <index> must be a value |
| from 0 through MAX_MULTIVIEW_BUFFERS_EXT. Otherwise, an |
| INVALID_OPERATION error is generated. If <location> is NONE, the |
| <index> is ignored. |
| |
| When FRAMEBUFFER_BINDING is zero, i.e. the default framebuffer, |
| <location> must be MULTIVIEW_EXT or NONE. If the buffer indicated by |
| <index> is missing, the error INVALID_OPERATION is generated. For |
| the default framebuffer, the initial setting for READ_BUFFER_EXT is |
| <location> of MULTIVIEW_EXT and <index> of zero. |
| |
| ReadBufferIndexedEXT generates an INVALID_OPERATION error if the GL |
| is bound to a framebuffer object. |
| |
| ReadPixels generates an INVALID_OPERATION error if it attempts to |
| select a color buffer while READ_BUFFER_EXT is none. |
| |
| New State |
| |
| Add the new Table 6.X "Framebuffer (State per framebuffer object)" : |
| |
| State Type Get Command Initial Description |
| --------------- ----- --------------- ------- ----------- |
| DRAW_BUFFER_EXT nxZ+ GetIntegeri_vEXT See 4.2.1 Multiview draw buffer |
| location and index |
| selected for the |
| specified color output |
| READ_BUFFER_EXT nxZ+ GetInteger See 4.3.1 Read source buffer |
| location and index |
| |
| Add the new Table 6.X "Framebuffer Dependent Values" : |
| |
| State Type Get Command Min Value Description |
| --------------- ----- --------------- --------- ----------- |
| MAX_MULTIVIEW_BUFFERS_EXT Z+ GetIntegerv 1 Number of multiview |
| draw buffers |
| |
| Issues |
| |
| 1. What should this extension be called? |
| |
| RESOLVED: multiview_draw_buffers. Multiview has come to be the |
| standard term to refer to stereoscopic and beyond buffer rendering |
| and this approach centers around the traditional usage of |
| a drawbuffers call to specify the buffer(s) to render to. |
| |
| 2. How should draw buffer bindings be queried? |
| |
| RESOLVED: A new indexed integer query function called |
| glGetIntegeri_vEXT. This extension adds an indexed binding for draw |
| buffers so it follows that an indexed query should be used to |
| retrieve the state that it sets. The name glGetIntegeri_vEXT is |
| chosen as it was in desktop GL to clarify the 'i' suffix |
| indicating an indexed call as opposed to 'i' indicating an integer |
| variant of a call accepting parameters of various types. |
| |
| 3. Should the <location> parameter of DrawBuffersIndexedEXT be removed? |
| |
| RESOLVED: No. It is useful when draw_buffers is supported. |
| |
| Revision History |
| Version 4, 25 Sept 2012 Clean up overview. Fix a few typographical |
| errors. |
| Version 3, 03 Sept 2011 EXTify. Remove ALL broadcast. |
| Add interactions for ES3 and non- |
| draw_buffers cases |
| Version 2, 02 Aug 2011 Responses to feedback. |
| Version 1, 14 April 2011 First draft. |
| |
