Difference between pages "GlDrawBuffer" and "GlDrawElements"

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'''_glDrawBuffer:''' specify which color buffers are to be drawn into
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'''_glDrawElements:''' render primitives from array data
  
  
 
{{PageSyntax}}
 
{{PageSyntax}}
  
::  SUB _glDrawBuffer (BYVAL mode AS _UNSIGNED LONG)
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:  SUB _glDrawElements (BYVAL mode AS _UNSIGNED LONG, BYVAL count AS LONG, BYVAL type AS _UNSIGNED LONG, indices AS _OFFSET)
::  void '''_glDrawBuffer'''(GLenum {{Parameter|mode}});
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:  void '''_glDrawElements'''(GLenum {{Parameter|mode}}, GLsizei {{Parameter|count}}, GLenum {{Parameter|type}}, const GLvoid * {{Parameter|indices}});
  
  
 
; mode
 
; mode
: Specifies up to four color buffers to be drawn into. Symbolic constants {{KW|_GL_NONE}}, {{KW|_GL_FRONT_LEFT}}, {{KW|_GL_FRONT_RIGHT}}, {{KW|_GL_BACK_LEFT}}, {{KW|_GL_BACK_RIGHT}}, {{KW|_GL_FRONT}}, {{KW|_GL_BACK}}, {{KW|_GL_LEFT}}, {{KW|_GL_RIGHT}}, and {{KW|_GL_FRONT_AND_BACK}} are accepted. The initial value is {{KW|_GL_FRONT}} for single-buffered contexts, and {{KW|_GL_BACK}} for double-buffered contexts.
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: Specifies what kind of primitives to render. Symbolic constants {{KW|_GL_POINTS}}, {{KW|_GL_LINE_STRIP}}, {{KW|_GL_LINE_LOOP}}, {{KW|_GL_LINES}}, {{KW|_GL_LINE_STRIP_ADJACENCY}}, {{KW|_GL_LINES_ADJACENCY}}, {{KW|_GL_TRIANGLE_STRIP}}, {{KW|_GL_TRIANGLE_FAN}}, {{KW|_GL_TRIANGLES}}, {{KW|_GL_TRIANGLE_STRIP_ADJACENCY}}, {{KW|_GL_TRIANGLES_ADJACENCY}} and {{KW|_GL_PATCHES}} are accepted.
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; count
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: Specifies the number of elements to be rendered.
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; type
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: Specifies the type of the values in {{Parameter|indices}}. Must be one of {{KW|_GL_UNSIGNED_BYTE}}, {{KW|_GL_UNSIGNED_SHORT}}, or {{KW|_GL_UNSIGNED_INT}}.
 +
; indices
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: Specifies a pointer to the location where the indices are stored.
  
  
 
{{PageDescription}}
 
{{PageDescription}}
  
When colors are written to the frame buffer, they are written into the color buffers specified by '''_glDrawBuffer'''. The specifications are as follows:
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'''_glDrawElements''' specifies multiple geometric primitives with very few subroutine calls. Instead of calling a GL function to pass each individual vertex, normal, texture coordinate, edge flag, or color, you can prespecify separate arrays of vertices, normals, and so on, and use them to construct a sequence of primitives with a single call to '''_glDrawElements'''.
  
; {{KW|_GL_NONE}}
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When '''_glDrawElements''' is called, it uses {{Parameter|count}} sequential elements from an enabled array, starting at {{Parameter|indices}} (interpreted as a byte count) to construct a sequence of geometric primitives. {{Parameter|mode}} specifies what kind of primitives are constructed and how the array elements construct these primitives. If more than one array is enabled, each is used.
: No color buffers are written.
 
; {{KW|_GL_FRONT_LEFT}}
 
: Only the front left color buffer is written.
 
; {{KW|_GL_FRONT_RIGHT}}
 
: Only the front right color buffer is written.
 
; {{KW|_GL_BACK_LEFT}}
 
: Only the back left color buffer is written.
 
; {{KW|_GL_BACK_RIGHT}}
 
: Only the back right color buffer is written.
 
; {{KW|_GL_FRONT}}
 
: Only the front left and front right color buffers are written. If there is no front right color buffer, only the front left color buffer is written.
 
; {{KW|_GL_BACK}}
 
: Only the back left and back right color buffers are written. If there is no back right color buffer, only the back left color buffer is written.
 
; {{KW|_GL_LEFT}}
 
: Only the front left and back left color buffers are written. If there is no back left color buffer, only the front left color buffer is written.
 
; {{KW|_GL_RIGHT}}
 
: Only the front right and back right color buffers are written. If there is no back right color buffer, only the front right color buffer is written.
 
; {{KW|_GL_FRONT_AND_BACK}}
 
: All the front and back color buffers (front left, front right, back left, back right) are written. If there are no back color buffers, only the front left and front right color buffers are written. If there are no right color buffers, only the front left and back left color buffers are written. If there are no right or back color buffers, only the front left color buffer is written.
 
If more than one color buffer is selected for drawing, then blending or logical operations are computed and applied independently for each color buffer and can produce different results in each buffer.
 
  
Monoscopic contexts include only ''left'' buffers, and stereoscopic contexts include both ''left'' and ''right'' buffers. Likewise, single-buffered contexts include only ''front'' buffers, and double-buffered contexts include both ''front'' and ''back'' buffers. The context is selected at GL initialization.
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Vertex attributes that are modified by '''_glDrawElements''' have an unspecified value after '''_glDrawElements''' returns. Attributes that aren't modified maintain their previous values.
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 +
 
 +
{{PageNotes}}
 +
 
 +
{{KW|_GL_LINE_STRIP_ADJACENCY}}, {{KW|_GL_LINES_ADJACENCY}}, {{KW|_GL_TRIANGLE_STRIP_ADJACENCY}} and {{KW|_GL_TRIANGLES_ADJACENCY}} are available only if the GL version is 3.2 or greater.
  
  
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{{KW|_GL_INVALID_ENUM}} is generated if {{Parameter|mode}} is not an accepted value.
 
{{KW|_GL_INVALID_ENUM}} is generated if {{Parameter|mode}} is not an accepted value.
  
{{KW|_GL_INVALID_OPERATION}} is generated if none of the buffers indicated by {{Parameter|mode}} exists.
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{{KW|_GL_INVALID_VALUE}} is generated if {{Parameter|count}} is negative.
 
 
  
{{PageUseWith}}
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{{KW|_GL_INVALID_OPERATION}} is generated if a geometry shader is active and {{Parameter|mode}} is incompatible with the input primitive type of the geometry shader in the currently installed program object.
  
{{KW|_glGet}} with argument {{KW|_GL_DRAW_BUFFER}}
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{{KW|_GL_INVALID_OPERATION}} is generated if a non-zero buffer object name is bound to an enabled array or the element array and the buffer object's data store is currently mapped.
  
  
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{{KW|_GL}}
 
{{KW|_GL}}
{{KW|_glBindFramebuffer}}, {{KW|_glBlendFunc}}, {{KW|_glColorMask}}, {{KW|_glDrawBuffers}}, {{KW|_glLogicOp}}
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{{KW|_glBindVertexArray}}, {{KW|_glDrawArrays}}, {{KW|_glDrawElementsBaseVertex}}, {{KW|_glDrawElementsIndirect}}, {{KW|_glDrawElementsInstanced}}, {{KW|_glDrawElementsInstancedBaseInstance}}, {{KW|_glDrawElementsInstancedBaseVertex}}, {{KW|_glDrawElementsInstancedBaseVertexBaseInstance}}, {{KW|_glDrawRangeElements}}, {{KW|_glDrawRangeElementsBaseVertex}}, {{KW|_glMultiDrawElements}}, {{KW|_glMultiDrawElementsBaseVertex}}, {{KW|_glMultiDrawElementsIndirect}}
  
  
 
{{PageCopyright}}
 
{{PageCopyright}}

Revision as of 15:33, 25 August 2013

_glDrawElements: render primitives from array data


Syntax

SUB _glDrawElements (BYVAL mode AS _UNSIGNED LONG, BYVAL count AS LONG, BYVAL type AS _UNSIGNED LONG, indices AS _OFFSET)
void _glDrawElements(GLenum mode, GLsizei count, GLenum type, const GLvoid * indices);


mode
Specifies what kind of primitives to render. Symbolic constants _GL_POINTS, _GL_LINE_STRIP, _GL_LINE_LOOP, _GL_LINES, _GL_LINE_STRIP_ADJACENCY, _GL_LINES_ADJACENCY, _GL_TRIANGLE_STRIP, _GL_TRIANGLE_FAN, _GL_TRIANGLES, _GL_TRIANGLE_STRIP_ADJACENCY, _GL_TRIANGLES_ADJACENCY and _GL_PATCHES are accepted.
count
Specifies the number of elements to be rendered.
type
Specifies the type of the values in indices. Must be one of _GL_UNSIGNED_BYTE, _GL_UNSIGNED_SHORT, or _GL_UNSIGNED_INT.
indices
Specifies a pointer to the location where the indices are stored.


Description

_glDrawElements specifies multiple geometric primitives with very few subroutine calls. Instead of calling a GL function to pass each individual vertex, normal, texture coordinate, edge flag, or color, you can prespecify separate arrays of vertices, normals, and so on, and use them to construct a sequence of primitives with a single call to _glDrawElements.

When _glDrawElements is called, it uses count sequential elements from an enabled array, starting at indices (interpreted as a byte count) to construct a sequence of geometric primitives. mode specifies what kind of primitives are constructed and how the array elements construct these primitives. If more than one array is enabled, each is used.

Vertex attributes that are modified by _glDrawElements have an unspecified value after _glDrawElements returns. Attributes that aren't modified maintain their previous values.


Notes:

_GL_LINE_STRIP_ADJACENCY, _GL_LINES_ADJACENCY, _GL_TRIANGLE_STRIP_ADJACENCY and _GL_TRIANGLES_ADJACENCY are available only if the GL version is 3.2 or greater.


Errors

_GL_INVALID_ENUM is generated if mode is not an accepted value.

_GL_INVALID_VALUE is generated if count is negative.

_GL_INVALID_OPERATION is generated if a geometry shader is active and mode is incompatible with the input primitive type of the geometry shader in the currently installed program object.

_GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to an enabled array or the element array and the buffer object's data store is currently mapped.


See also

_GL _glBindVertexArray, _glDrawArrays, _glDrawElementsBaseVertex, _glDrawElementsIndirect, _glDrawElementsInstanced, _glDrawElementsInstancedBaseInstance, _glDrawElementsInstancedBaseVertex, _glDrawElementsInstancedBaseVertexBaseInstance, _glDrawRangeElements, _glDrawRangeElementsBaseVertex, _glMultiDrawElements, _glMultiDrawElementsBaseVertex, _glMultiDrawElementsIndirect


Copyright: 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License.
For details, see http://oss.sgi.com/projects/FreeB/.



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