| '''OpenGL extension ARB.clip_control |
| |
| This module customises the behaviour of the |
| OpenGL.raw.GL.ARB.clip_control to provide a more |
| Python-friendly API |
| |
| Overview (from the spec) |
| |
| This extension provides additional clip control modes to configure how |
| clip space is mapped to window space. This extension's goal is to 1) |
| allow OpenGL to effectively match Direct3D's coordinate system |
| conventions, and 2) potentially improve the numerical precision of the Z |
| coordinate mapping. |
| |
| Developers interested in this functionality may be porting content |
| from Direct3D to OpenGL and/or interested in improving the numerical |
| accuracy of depth testing, particularly with floating-point depth |
| buffers. |
| |
| OpenGL's initial and conventional clip control state is configured by: |
| |
| glClipControl(GL_LOWER_LEFT, GL_NEGATIVE_ONE_TO_ONE); |
| |
| where geometry with (x,y) normalized device coordinates of (-1,-1) |
| correspond to the lower-left corner of the viewport and the near and far |
| planes correspond to z normalized device coordinates of -1 and +1, |
| respectively. |
| |
| This extension can be used to render content used in a Direct3D |
| application in OpenGL in a straightforward way without modifying vertex or |
| matrix data. When rendering into a window, the command |
| |
| glClipControl(GL_LOWER_LEFT, GL_ZERO_TO_ONE); |
| |
| configures the near clip plane to correspond to a z normalized device |
| coordinate of 0 as in Direct3D. Geometry with (x,y) normalized device |
| coordinates of (-1,-1) correspond to the lower-left corner of the viewport |
| in Direct3D, so no change relative to OpenGL conventions is needed there. |
| Other state related to screen-space coordinates may need to be modified |
| for the application to map from Direct3D to OpenGL window coordinate |
| conventions. For example, the viewport rectangle in Direct3D needs to be |
| inverted within the window to work properly in OpenGL windowed rendering: |
| |
| glViewport(d3d_viewport_x, |
| window_height - (d3d_viewport_y + d3d_viewport_height), |
| d3d_viewport_width, d3d_viewport_height); |
| |
| When rendering Direct3D content into a framebuffer object in OpenGL, there |
| is one complication -- how to get a correct image *out* of the related |
| textures. Direct3D applications would expect a texture coordinate of |
| (0,0) to correspond to the upper-left corner of a rendered image, while |
| OpenGL FBO conventions would map (0,0) to the lower-left corner of the |
| rendered image. For applications wishing to use Direct3D content with |
| unmodified texture coordinates, the command |
| |
| glClipControl(GL_UPPER_LEFT, GL_ZERO_TO_ONE); |
| |
| configures the OpenGL to invert geometry vertically inside the viewport. |
| Content at the top of the viewport for Direct3D will be rendered to the |
| bottom of the viewport from the point of view of OpenGL, but will have a |
| <t> texture coordinate of zero in both cases. When operating in this |
| mode, applications need not invert the programmed viewport rectangle as |
| recommended for windowed rendering above. |
| |
| Applications happy with OpenGL's origin conventions but seeking |
| potentially improved depth precision can configure clip controls using: |
| |
| glClipControl(GL_LOWER_LEFT, GL_ZERO_TO_ONE); |
| |
| to avoid the loss of precision from the DepthRange transformation |
| (which by default is z_window = z_ndc * 0.5 + 0.5). |
| |
| The official definition of this extension is available here: |
| http://www.opengl.org/registry/specs/ARB/clip_control.txt |
| ''' |
| from OpenGL import platform, constant, arrays |
| from OpenGL import extensions, wrapper |
| import ctypes |
| from OpenGL.raw.GL import _types, _glgets |
| from OpenGL.raw.GL.ARB.clip_control import * |
| from OpenGL.raw.GL.ARB.clip_control import _EXTENSION_NAME |
|
|
| def glInitClipControlARB(): |
| '''Return boolean indicating whether this extension is available''' |
| from OpenGL import extensions |
| return extensions.hasGLExtension( _EXTENSION_NAME ) |
|
|
|
|
| |
