| | '''OpenGL extension ARB.fragment_coord_conventions |
| | |
| | This module customises the behaviour of the |
| | OpenGL.raw.GL.ARB.fragment_coord_conventions to provide a more |
| | Python-friendly API |
| | |
| | Overview (from the spec) |
| | |
| | This extension provides alternative conventions for the fragment |
| | coordinate XY location available for programmable fragment processing. |
| | |
| | The scope of this extension deals *only* with how the fragment |
| | coordinate XY location appears during programming fragment processing. |
| | Beyond the scope of this extension are coordinate conventions used |
| | for rasterization or transformation. |
| | |
| | In the case of the coordinate conventions for rasterization and |
| | transformation, some combination of the viewport, depth range, culling |
| | state, and projection matrix state can be reconfigured to adopt other |
| | arbitrary clip-space and window-space coordinate space conventions. |
| | Adopting other clip-space and window-space conventions involves |
| | adjusting existing OpenGL state. However it is non-trivial to massage |
| | an arbitrary fragment shader or program to adopt a different |
| | window-space coordinate system because such shaders are encoded in |
| | various textual representations. |
| | |
| | The dominant 2D and 3D rendering APIs make two basic choices of |
| | convention when locating fragments in window space. |
| | |
| | The two choices are: |
| | |
| | 1) Is the origin nearest the lower-left- or upper-left-most pixel |
| | of the window? |
| | |
| | 2) Is the (x,y) location of the pixel nearest the origin at (0,0) |
| | or (0.5,0.5)? |
| | |
| | OpenGL assumes a lower-left origin for window coordinates and assumes |
| | pixel centers are located at half-pixel coordinates. This means |
| | the XY location (0.5,0.5) corresponds to the lower-left-most pixel |
| | in a window. |
| | |
| | Other window coordinate conventions exist for other rendering APIs. |
| | X11, GDI, and Direct3D version through DirectX 9 assume an upper-left |
| | window origin and locate pixel centers at integer XY values. |
| | By this alternative convention, the XY location (0,0) corresponds |
| | to the upper-left-most pixel in a window. |
| | |
| | Direct3D for DirectX 10 assumes an upper-left origin (as do prior |
| | DirectX versions) yet assumes half-pixel coordinates (unlike prior |
| | DirectX versions). By the DirectX 10 convention, the XY location |
| | (0.5,0.5) corresponds to the upper-left-most pixel in a window. |
| | |
| | Fragment shaders can directly access the location of a given |
| | processed fragment in window space. We call this location the |
| | "fragment coordinate". |
| | |
| | This extension provides a means for fragment shaders written in GLSL |
| | or OpenGL assembly extensions to specify alternative conventions |
| | for determining the fragment coordinate value accessed during |
| | programmable fragment processing. |
| | |
| | The motivation for this extension is to provide an easy, efficient |
| | means for fragment shaders accessing a fragment's window-space |
| | location to adopt the fragment coordinate convention for which the |
| | shader was originally written. |
| | |
| | The official definition of this extension is available here: |
| | http://www.opengl.org/registry/specs/ARB/fragment_coord_conventions.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.fragment_coord_conventions import * |
| | from OpenGL.raw.GL.ARB.fragment_coord_conventions import _EXTENSION_NAME |
| |
|
| | def glInitFragmentCoordConventionsARB(): |
| | '''Return boolean indicating whether this extension is available''' |
| | from OpenGL import extensions |
| | return extensions.hasGLExtension( _EXTENSION_NAME ) |
| |
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| |
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| | |
