Difference between revisions of "Vertex Shader/Defined Outputs"

From OpenGL Wiki
Jump to navigation Jump to search
(Not clip plane, but clipping half-spaces.)
(Clamping of point sizes.)
Line 17: Line 17:
 
: the clip-space output position of the current vertex.
 
: the clip-space output position of the current vertex.
 
; {{code|gl_PointSize}}
 
; {{code|gl_PointSize}}
: the pixel width/height of the point being rasterized. It only has a meaning when rendering [[Point Primitive|point primitives]].
+
: the pixel width/height of the point being rasterized. It only has a meaning when rendering [[Point Primitive|point primitives]]. It will be clamped to the {{enum|GL_POINT_SIZE_RANGE}}.
 
; {{code|gl_ClipDistance}}
 
; {{code|gl_ClipDistance}}
 
: allows the shader to set the distance from the vertex to each [[User-Defined Clip Plane|user-defined clipping half-space]]. A non-negative distance means that the vertex is inside/behind the clip plane, and a negative distance means it is outside/in front of the clip plane. Each element in the array is one clip plane. In order to use this variable, the user must manually redeclare it with an explicit size.
 
: allows the shader to set the distance from the vertex to each [[User-Defined Clip Plane|user-defined clipping half-space]]. A non-negative distance means that the vertex is inside/behind the clip plane, and a negative distance means it is outside/in front of the clip plane. Each element in the array is one clip plane. In order to use this variable, the user must manually redeclare it with an explicit size.

Revision as of 00:59, 8 December 2015

Vertex Shaders have the following predefined outputs.

out gl_PerVertex
{
  vec4 gl_Position;
  float gl_PointSize;
  float gl_ClipDistance[];
};

gl_PerVertex defines an interface block for outputs. The block is defined without an instance name, so that prefixing the names is not required.

These variables only take on the meanings below if this shader is the last active Vertex Processing stage, and if rasterization is still active (ie: GL_RASTERIZER_DISCARD is not enabled). The text below explains how the Vertex Post-Processing system uses the variables. These variables may not be redeclared with interpolation qualifiers.

gl_Position
the clip-space output position of the current vertex.
gl_PointSize
the pixel width/height of the point being rasterized. It only has a meaning when rendering point primitives. It will be clamped to the GL_POINT_SIZE_RANGE.
gl_ClipDistance
allows the shader to set the distance from the vertex to each user-defined clipping half-space. A non-negative distance means that the vertex is inside/behind the clip plane, and a negative distance means it is outside/in front of the clip plane. Each element in the array is one clip plane. In order to use this variable, the user must manually redeclare it with an explicit size.