skia / external / github.com / KhronosGroup / OpenGL-Registry / refs/heads/11723-workgroup / . / extensions / ATI / ATI_pn_triangles.txt

Name | |

ATI_pn_triangles | |

Name Strings | |

GL_ATI_pn_triangles | |

Contact | |

Dan Ginsburg, AMD (dan.ginsburg 'at' amd.com) | |

Alex Vlachos | |

Version | |

Last Modified Date: November 4, 2006 | |

Revision: 1.2 | |

Number | |

246 | |

Dependencies | |

ARB_vertex_program and EXT_vertex_shader affect the definition of | |

this extension. | |

Overview | |

ATI_pn_triangles provides a path for enabling the GL to internally | |

tessellate input geometry into curved patches. The extension allows the | |

user to tune the amount of tessellation to be performed on each triangle as | |

a global state value. The intent of PN Triangle tessellation is | |

typically to produce geometry with a smoother silhouette and more organic | |

shape. | |

The tessellated patch will replace the triangles input into the GL. | |

The GL will generate new vertices in object-space, prior to geometry | |

transformation. Only the vertices and normals are required to produce | |

proper results, and the rest of the information per vertex is interpolated | |

linearly across the patch. | |

Issues | |

(1) Should this extension mandate the algorithm used to perform | |

tessellation? | |

RESOLVED: Yes, both for performance and so that the resultant | |

geometry is consistent across implementations. | |

(2) What geometry modes will be supported for tessellation besides | |

TRIANGLE based primitives? | |

RESOLVED: None, only triangle based primitives: triangles, fans, | |

and strips. | |

(3) How does this extension interact with the EXT_vertex_shader and | |

ARB_vertex_program programmable vertex shader extensions? | |

RESOLVED: The PN Triangle tessellation algorithm requires the | |

presence of both vertex position and normal. Therefore, if an | |

application enables PN Triangle tessellation and has a programmable | |

vertex shader enabled, that shader should export the fixed-function | |

equivalent of position and normal. If the shader does not export | |

either the position or normal, then the results of PN Triangle | |

tessellation are undefined. | |

New Procedure and Functions | |

PNTrianglesiATI(enum pname, int param) | |

PNTrianglesfATI(enum pname, float param) | |

New Tokens | |

Accepted by the <target> Enable, Disable, and IsEnabled: | |

PN_TRIANGLES_ATI 0x87F0 | |

Accepted by the <value> parameter of GetBooleanv, GetIntegerv, | |

GetFloatv, and GetDoublev: | |

MAX_PN_TRIANGLES_TESSELATION_LEVEL_ATI 0x87F1 | |

Accepted by the <pname> parameter of PNTriangles[if]ATI, | |

GetBooleanv, GetDoublev, GetFloatv, and GetIntegerv: | |

PN_TRIANGLES_POINT_MODE_ATI 0x87F2 | |

PN_TRIANGLES_NORMAL_MODE_ATI 0x87F3 | |

PN_TRIANGLES_TESSELATION_LEVEL_ATI 0x87F4 | |

Accepted by the <param> parameter of PNTriangles[if]ATI | |

when <pname> is PN_TRIANGLES_POINT_MODE_ATI: | |

PN_TRIANGLES_POINT_MODE_LINEAR_ATI 0x87F5 | |

PN_TRIANGLES_POINT_MODE_CUBIC_ATI 0x87F6 | |

Accepted by the <param> parameter of PNTriangles[if]ATI | |

when <pname> is PN_TRIANGLES_NORMAL_MODE_ATI: | |

PN_TRIANGLES_NORMAL_MODE_LINEAR_ATI 0x87F7 | |

PN_TRIANGLES_NORMAL_MODE_QUADRATIC_ATI 0x87F8 | |

Additions to Chapter 2 of the OpenGL 1.2.1 Specification (Operation) | |

None | |

Additions to Chapter 3 if the OpenGL 1.2.1 Specification (Rasterization): | |

Add a new section "PN Triangles" after "3.10 Fog" and before "3.11 | |

Antialiasing Application": | |

"3.11 PN Triangles | |

When PN Triangle generation is enabled, each triangle-based geometric | |

primitive is replaced with a new curved surface using the primitive | |

vertices as control points. The intent of PN Triangles | |

are to take a set of triangle-based geometry and algorithmically | |

tessellate it into a more organic shape with a smoother silhouette. | |

The new surface can either linearly or quadratically interpolate the | |

normals across the patch. The vertices can be either linearly or | |

cubically interpolated across the patch. Linear interpolation | |

of the points would be useful for getting more sample points for | |

lighting on the same geometric shape. All other vertex information | |

(colors, texture coordinates, fog coordinates, and vertex weights) are | |

interpolated linearly across the patch. | |

PN Triangle generation is enabled and disabled with the Enable and Disable | |

commands using the symbolic constant PN_TRIANGLES_ATI. The level of | |

tessellation to be performed is specified as the number of evaluation | |

points on each edge. Specifying 0 would use the original triangle, 1 | |

would generate one new point on each edge of the triangle, and so forth. | |

The tessellation level and normal generation mode are specified with: | |

void PNTriangles{if}ATI(enum pname, T param) | |

If <pname> is PN_TRIANGLES_NORMAL_MODE_ATI then <param> must be one of the | |

symbolic constants PN_TRIANGLES_NORMAL_MODE_LINEAR_ATI or | |

PN_TRIANGLES_NORMAL_MODE_QUADRATIC_ATI which will select linear or | |

quadratic normal interpolation respectively. If <pname> is | |

PN_TRIANGLES_POINT_MODE_ATI then <param> must be one of the symbolic | |

constants PN_TRIANGLES_POINT_MODE_LINEAR_ATI or | |

PN_TRIANGLES_POINT_MODE_CUBIC_ATI which will select linear or cubic | |

interpolation respectively. If <pname> is | |

PN_TRIANGLES_TESSELATION_LEVEL_ATI then <param> should be a value | |

specifying the number of evaluation points on each edge. This value must be | |

greater than 0 and less than or equal to the value given by | |

MAX_PN_TRIANGLES_TESSELATION_LEVEL_ATI. An INVALID_VALUE error will be | |

generated if the value for <param> is less than zero or greater than the max | |

value. | |

If either VERTEX_SHADER_EXT or VERTEX_SHADER_ARB are enabled, then the | |

shader specified by the application must export both the position and normal | |

in order for PN triangle tessellation to work correctly. If either the | |

position or normal are not exported by the vertex shader then the result of | |

PN triangle tessellation is undefined." | |

Additions to Chapter 4: | |

None | |

Additions to Chapter 5: | |

None | |

Additions to Chapter 6: | |

None | |

Additions to the GLX Specification | |

None | |

GLX Protocol | |

None | |

Errors | |

INVALID_VALUE is generated if the <param> parameter for | |

PNTriangles{if}ATI is less than zero or greater than | |

the value given for MAX_PN_TRIANGLES_TESSELATION_LEVEL_ATI | |

when <pname> is PN_TRIANGLES_TESSELATION_LEVEL_ATI. | |

New State | |

New table after Table 6.6 Fog: | |

"Table 6.7 PN Triangles: | |

Get Value Get Command Type Initial Value Attribute | |

--------- ----------- ---- ------------- --------- | |

PN_TRIANGLES_ATI IsEnabled B False PN Triangles/enable | |

PN_TRIANGLES_NORMAL_MODE_ATI GetIntegerv Z2 PN_TRIANGLES_NORMAL_MODE_QUADRATIC_ATI PN Triangles | |

PN_TRIANGLES_POINT_MODE_ATI GetIntegerv Z2 PN_TRIANGLES_POINT_MODE_CUBIC_ATI PN Triangles | |

PN_TRIANGLES_TESSELATION_LEVEL_ATI GetIntegerv Z+ 1 PN Triangles | |

Modified state in Table 6.25: | |

Get Value Get Command Type Minimum Value Attribute | |

--------- ----------- ---- ------------ --------- | |

MAX_PN_TRIANGLES_TESSELATION_LEVEL_ATI GetIntegerv Z+ 1 - | |

" | |

New Implementation Dependent State | |

None | |

Revision History | |

Date: 11/4/2006 | |

Revision: 1.2 | |

- Updated contact info after ATI/AMD merger. | |

Date: 11/11/2002 | |

Revision: 1.1 | |

- Added issue and documentation that describes interaction between | |

PN Triangles and vertex shaders. | |

Date: 8/21/2001 | |

Revision: 1.0 | |

- First published version | |