| Name |
| |
| NV_read_depth |
| NV_read_stencil |
| NV_read_depth_stencil |
| |
| Name Strings |
| |
| GL_NV_read_depth |
| GL_NV_read_stencil |
| GL_NV_read_depth_stencil |
| |
| Contact |
| |
| Greg Roth, NVIDIA Corporation (groth 'at' nvidia.com) |
| |
| Contributors |
| |
| Koji Ashida, NVIDIA Corporation |
| Gregory Prisament, NVIDIA Corporation |
| Greg Roth, NVIDIA Corporation |
| |
| Status |
| |
| Complete. |
| |
| Version |
| |
| Last Modified Date: June 07, 2011 |
| NVIDIA Revision: 4.0 |
| |
| Number |
| |
| OpenGL ES Extension #94 |
| |
| Dependencies |
| |
| Written against the OpenGL ES 2.0 Specification. |
| |
| NV_depth_buffer_float2 affects this extension. |
| |
| NV_read_depth_stencil requires OES_packed_depth_stencil. |
| |
| Overview |
| |
| Unextended OpenGL-ES 2.0 only supports using ReadPixels to read from the |
| default color buffer of the currently-bound framebuffer. However, it is |
| useful for debugging to be able to read from depth and stencil buffers. |
| This extension re-introduces these features into OpenGL-ES 2.0. |
| |
| This document describes several extensions in order to allow an |
| implementation to support a subset of the total functionality. |
| |
| The NV_read_depth extension allows reading from the depth buffer using |
| ReadPixels. |
| |
| The NV_read_stencil extension allows reading from the stencil buffer using |
| ReadPixels. |
| |
| The NV_read_depth_stencil extension allows reading from packed |
| depth-stencil buffers using ReadPixels. |
| |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| None. |
| |
| Changes to Chapter 4 of the OpenGL ES 2.0 Specification |
| (Per-Fragment Operations and the Framebuffer) |
| |
| |
| Section 4.3.1 (Reading Pixels), replace description of ReadPixels: |
| |
| The arguments after x and y to ReadPixels are those described in |
| section 3.6.2 defining pixel rectangles. The pixel storage modes |
| that apply to ReadPixels are summarized in Table 4.3. |
| |
| Section 4.3.1 (Reading Pixels) subsection "Obtaining Pixels from |
| the Framebuffer", replace the first paragraph with: |
| |
| If the <format> is DEPTH_COMPONENT, then values are obtained |
| from the depth buffer. If there is no depth buffer, the error |
| INVALID_OPERATION occurs. If the <type> is not UNSIGNED_SHORT, |
| FLOAT, or UNSIGNED_INT_24_8_OES then the error INVALID_ENUM |
| occurs. If the <type> is FLOAT and the depth buffer is not a |
| float buffer, an INVALID_OPERATION error occurs. If the <type> |
| is UNSIGNED_SHORT or UNSIGNED_INT_24_8_OES and the depth buffer |
| is a float buffer, an INVALID_OPERATION error occurs. When the |
| <type> is UNSIGNED_INT_24_8_OES the values read into the 8 |
| stencil bits are undefined. |
| |
| If the <format> is DEPTH_STENCIL_OES, then values are taken from |
| both the depth buffer and the stencil buffer. If there is no |
| depth buffer or if there is no stencil buffer, then the error |
| INVALID_OPERATION occurs. If the <type> is not UNSIGNED_INT_24_- |
| 8_OES or FLOAT_32_UNSIGNED_INT_24_8_REV_NV, then the error |
| INVALID_ENUM occurs. If the <type> is FLOAT_32_UNSIGNED_INT_24_- |
| 8_REV_NV and the depth buffer is not a float buffer, an INVALID_- |
| OPERATION error occurs. If the <type> is UNSIGNED_INT_24_8_OES |
| and the depth buffer is a float buffer, an INVALID_OPERATION |
| error occurs. |
| |
| If the <format> is STENCIL_INDEX, then values are taken from |
| the stencil buffer. If there is no stencil buffer, then the |
| error INVALID_OPERATION occurs. If the <type> is not |
| UNSIGNED_BYTE, then the error INVALID_ENUM occurs. |
| |
| If <format> is a color format, then red, green, blue, and alpha |
| values are obtained from the color buffer at each pixel |
| location. If the framebuffer does not support alpha values then |
| the value that is obtained is 1.0. Only two combinations of |
| color format and type are accepted. The first is format RGBA and |
| type UNSIGNED_BYTE. The second is an implementation-chosen |
| format from among those defined in table 3.4, excluding formats |
| LUMINANCE and LUMINANCE_ALPHA. The values of format and type for |
| this format may be determined by calling GetIntegerv with the |
| symbolic constants IMPLEMENTATION_COLOR_READ_FORMAT and |
| IMPLEMENTATION_COLOR_READ_TYPE, respectively. The implementation- |
| chosen format may vary depending on the format of the currently |
| bound rendering surface. Unsupported combinations of format and |
| type will generate an INVALID_OPERATION error. |
| |
| Dependencies on NV_read_depth: |
| |
| If NV_read_depth is not supported, the paragraph in "Obtaining Pixels |
| from the Framebuffer" describing behavior when the <format> is |
| DEPTH_COMPONENT is omitted. |
| |
| Dependencies on NV_read_stencil: |
| |
| If NV_read_stencil is not supported, the paragraph in "Obtaining |
| Pixels from the Framebuffer" describing behavior "when the <format> |
| is STENCIL_INDEX" is omitted. |
| |
| Dependencies on NV_read_depth_stencil: |
| |
| If NV_read_depth_stencil is not supported, the paragraph in |
| "Obtaining Pixels from the Framebuffer" describing behavior "when |
| the <format> is DEPTH_STENCIL_OES is omitted and UNSIGNED_INT_24_8_EXT is not an |
| accepted <value> when <format> is DEPTH_COMPONENT. |
| |
| Dependencies on NV_depth_buffer_float2: |
| |
| If NV_depth_buffer_float2 is not supported, FLOAT is not an accepted |
| <value> when <format> is DEPTH_COMPONENT and FLOAT_32_UNSIGNED_INT_- |
| 24_8_REV_NV is not an accepted <value> when <format> is DEPTH_- |
| STENCIL_OES. |
| |
| Issues |
| |
| 1. Do we need to be able to read stencil buffers individually? |
| |
| On platforms that easily support reading stencil buffers |
| individually, it is useful for debugging. However, we do not want |
| to require that it is supported on platforms using packed depth- |
| stencil buffers. Therefore we use multiple extension names. |
| |
| 2. Should we have FRONT/BACK, LEFT/RIGHT buffer enums for <mode> |
| parameter of ReadBufferNV to be used with window system provided |
| framebuffers? |
| |
| OpenGL ES 2.0 does not support stereo framebuffers, so for now we |
| only support FRONT and BACK. |
| |
| 3. Should this extension add reading of coverage samples? |
| |
| No. That should be left to the EGL_NV_coverage_sample |
| specification. |
| |
| 4. How does this extension interact with NV_read_buffer? |
| |
| NV_read_buffer adds support for the ReadBufferNV command, which is |
| used to select which color buffer to read from. It does not |
| affect the behavior of this extension, since all framebuffers have |
| at most one depth and one stencil buffer. |
| |
| |
| Revision History |
| |
| Rev. Date Author Changes |
| ---- -------- --------- ------------------------------------- |
| 4 06/01/11 groth Mostly rewrote spec edits to better |
| match the spec and more clearly |
| describe behavior. Reformatted. |
| 3 03/22/09 gprisament Split from NV_read_buffer. |
| Broken into several extension names. |
| Re-wrote overview section. |
| 2 07/03/08 kashida Change to depend on |
| NV_packed_depth_stencil2 |
| 1 06/10/07 kashida First revision. |
| |
