Difference between revisions of "Vertex Shader/Defined Outputs"

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(Centralizing vertex shader outputs.)
 
(Better description of them.)
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{{code|gl_PerVertex}} defines an [[Interface Block (GLSL)|interface block]] for outputs. The block is defined without an instance name, so that prefixing the names is not required.
 
{{code|gl_PerVertex}} defines an [[Interface Block (GLSL)|interface block]] for outputs. The block is defined without an instance name, so that prefixing the names is not required.
  
{{code|gl_Position}} is the output position of the current vertex. If the vertex shader is the last active shader stage before the fragment shader, and rasterization is still active (ie: {{enum|GL_RASTERIZER_DISCARD}} is not enabled), then the vertex shader must write to this variable. In that case, this value should be the clip-space vertex position.
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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: {{enum|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.
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{{code|gl_Position}} is the clip-space output position of the current vertex.
  
 
{{code|gl_PointSize}} is the pixel width/height of the point being rasterized. It is only necessary to write to this when rendering [[Primitive#Point_Primitives|point primitives]].
 
{{code|gl_PointSize}} is the pixel width/height of the point being rasterized. It is only necessary to write to this when rendering [[Primitive#Point_Primitives|point primitives]].
  
{{code|gl_ClipDistance}} allows the shader to set the distance from a vertex to each clip plane. A positive 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. In order to use this variable, the user must manually redeclare it with an explicit size.
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{{code|gl_ClipDistance}} allows the shader to set the distance from the vertex to each clip plane. A positive 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. In order to use this variable, the user must manually redeclare it with an explicit size.

Revision as of 20:09, 25 July 2013

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​ is the clip-space output position of the current vertex.

gl_PointSize​ is the pixel width/height of the point being rasterized. It is only necessary to write to this when rendering point primitives.

gl_ClipDistance​ allows the shader to set the distance from the vertex to each clip plane. A positive 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. In order to use this variable, the user must manually redeclare it with an explicit size.