GlDrawElements: Difference between revisions

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(Created page with "'''_glDrawElements:''' render primitives from array data {{PageSyntax}} : SUB _glDrawElements (BYVAL mode AS _UNSIGNED LONG, BYVAL count AS LONG, BYVAL type AS _UNSIGNED LONG, indices AS _OFFSET) : void '''_glDrawElements'''(GLenum {{Parameter|mode}}, GLsizei {{Parameter|count}}, GLenum {{Parameter|type}}, const GLvoid * {{Parameter|indices}}); ; mode : Specifies what kind of primitives to render. Symbolic constants {{KW|_GL_POINTS}}, {{KW|_GL_LINE_STRIP}}, {{KW|_...")
 
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'''_glDrawElements:''' render primitives from array data
{{DISPLAYTITLE:_glDrawElements}}
The '''_glDrawElements''' statement renders primitives from array data.




{{PageSyntax}}
{{PageSyntax}}
: [[_glDrawElements]] GLenum {{Parameter|mode}}, GLsizei {{Parameter|count}}, GLenum {{Parameter|type}}, const GLvoid {{Parameter|*indices}}


:  SUB _glDrawElements (BYVAL mode AS _UNSIGNED LONG, BYVAL count AS LONG, BYVAL type AS _UNSIGNED LONG, indices AS _OFFSET)
:  void '''_glDrawElements'''(GLenum {{Parameter|mode}}, GLsizei {{Parameter|count}}, GLenum {{Parameter|type}}, const GLvoid * {{Parameter|indices}});


 
{{PageParameters}}
; mode
* OpenGL is using its own set of variable types to describe its command parameters.
: 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.
* Use the following table to find the respective QB64 [[Variable Types]].
; count
{{OpenGLTypesPlugin}}
: Specifies the number of elements to be rendered.
; type
: 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
: Specifies a pointer to the location where the indices are stored.




{{PageDescription}}
{{PageDescription}}
 
* OpenGL's documentation is available in several places, so we won't reproduce it here for another time.
'''_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'''.
* The full description for this command can be found at [https://learn.microsoft.com/en-us/windows/win32/opengl/gldrawelements Microsoft Docs] and is also valid for QB64 usage.
 
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.
 
Vertex attributes that are modified by '''_glDrawElements''' have an unspecified value after '''_glDrawElements''' returns. Attributes that aren't modified maintain their previous values.
 
 
{{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.
 
 
{{PageErrors}}
 
{{KW|_GL_INVALID_ENUM}} is generated if {{Parameter|mode}} is not an accepted value.
 
{{KW|_GL_INVALID_VALUE}} is generated if {{Parameter|count}} is negative.
 
{{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|_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.




{{PageSeeAlso}}
{{PageSeeAlso}}
 
* [[_GL|SUB _GL]]
[[_GL|SUB _GL]]
* [[_glArrayElement]], [[_glBegin]], [[_glColorPointer]], [[_glDrawArrays]]
{{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}}
* [[_glEdgeFlagPointer]], [[_glEnd]], [[_glGetPointerv]], [[_glIndexPointer]]
* [[_glNormalPointer]], [[_glTexCoordPointer]], [[_glVertexPointer]]




{{PageCopyright}}
{{PageNavigation}}

Latest revision as of 00:50, 28 January 2023

The _glDrawElements statement renders primitives from array data.


Syntax

_glDrawElements GLenum mode, GLsizei count, GLenum type, const GLvoid *indices


Parameters

  • OpenGL is using its own set of variable types to describe its command parameters.
  • Use the following table to find the respective QB64 Variable Types.
   Table 2: Relations between the OpenGL variable types vs. C/C++ and QB64.
 ┌──────────────┬────────────────┬──────────────────────────────────────────┐
 │    OpenGL    │     C/C++      │     QB64                                 │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLenum       │ unsigned int   │ _UNSIGNED LONG                           │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLboolean    │ unsigned char  │ _UNSIGNED _BYTE                          │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLbitfield   │ unsigned int   │ _UNSIGNED LONG                           │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLbyte       │ signed char    │ _BYTE                                    │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLshort      │ short          │ INTEGER                                  │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLint        │ int            │ LONG                                     │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLsizei      │ int            │ LONG                                     │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLubyte      │ unsigned char  │ _UNSIGNED _BYTE                          │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLushort     │ unsigned short │ _UNSIGNED INTEGER                        │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLuint       │ unsigned int   │ _UNSIGNED LONG                           │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLfloat      │ float          │ SINGLE                                   │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLclampf     │ float          │ SINGLE                                   │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLdouble     │ double         │ DOUBLE                                   │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLclampd     │ double         │ DOUBLE                                   │
 ├──────────────┼────────────────┼──────────────────────────────────────────┤
 │ GLvoid   (1) │ void           │ _OFFSET(any fixed lenght string or _BYTE │
 │              │                │         array element)                   │
 └──────────────┴────────────────┴──────────────────────────────────────────┘
 Note: If a parameter has an asterisk (*) in front, then it's a pointer to
       the designated OpenGL variable type, rather than a value of that type.
       Those must be passed using the _OFFSET(...) notation.

 E.g.  GLuint *anyParam is actually the offset of a _UNSIGNED LONG (~&)
       variable or array, which must be passed as _OFFSET(anyVar~&) or
       _OFFSET(anyArr~&()) respectively.

  (1)  This type is regularly only used for pointers (with asterisk (*)) to
       any byte sized memory data, hence _BYTE or fixed length strings.


Description

  • OpenGL's documentation is available in several places, so we won't reproduce it here for another time.
  • The full description for this command can be found at Microsoft Docs and is also valid for QB64 usage.


See also


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