GlClear: Difference between revisions

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(Created page with "'''_glClear:''' clear buffers to preset values {{PageSyntax}} :: SUB _glClear (BYVAL mask AS _UNSIGNED LONG) :: void '''_glClear'''(GLbitfield {{Parameter|mask}}); {{PageParameters}} * ''mask'' that indicate the buffer OR buffers to be cleared. The three masks are _GL_COLOR_BUFFER_BIT, _GL_DEPTH_BUFFER_BIT, and _GL_STENCIL_BUFFER_BIT. {{PageDescription}} * _glClear sets the bitplane area of the window to values previously sele...")
 
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'''_glClear:''' clear buffers to preset values
{{DISPLAYTITLE:_glClear}}
The '''_glClear''' statement clears buffers to preset values.




{{PageSyntax}}
{{PageSyntax}}
 
: [[_glClear]] GLbitfield {{Parameter|mask}}
:: [[SUB]] _glClear ([[BYVAL]] mask AS [[_UNSIGNED]] [[LONG]])
::  void '''_glClear'''(GLbitfield {{Parameter|mask}});




{{PageParameters}}
{{PageParameters}}
* ''mask'' that indicate the buffer [[OR]] buffers to be cleared. The three masks are [[_GL_COLOR_BUFFER_BIT]], [[_GL_DEPTH_BUFFER_BIT]], and [[_GL_STENCIL_BUFFER_BIT]].
* 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]].
{{OpenGLTypesPlugin}}




{{PageDescription}}
{{PageDescription}}
 
* OpenGL's documentation is available in several places, so we won't reproduce it here for another time.
* [[_glClear]] sets the bitplane area of the window to values previously selected by [[_glClearColor]], [[glClearDepth]], and [[_glClearStencil]].  
* The full description for this command can be found at [https://learn.microsoft.com/en-us/windows/win32/opengl/glclear Microsoft Docs] and is also valid for QB64 usage.
* Multiple color buffers can be cleared simultaneously by selecting more than one buffer at a time using [[_glDrawBuffer]].
* The pixel ownership test, the scissor test, dithering, and the buffer writemasks affect the operation of [[_glClear]]. The scissor box bounds the cleared region. Alpha function, blend function, logical operation, stenciling, texture mapping, and depth-buffering are ignored by [[_glClear]].
 
* [[_glClear]] takes a single argument that is the bitwise OR of several values indicating which buffer is to be cleared. The values are as follows:
 
::: [[_GL_COLOR_BUFFER_BIT]]: Indicates the buffers currently enabled for color writing.
::: [[_GL_DEPTH_BUFFER_BIT]]: Indicates the depth buffer.
::: [[_GL_STENCIL_BUFFER_BIT]]: Indicates the stencil buffer.
 
* The value to which each buffer is cleared depends on the setting of the clear value for that buffer.
 
 
{{PageNotes}}
 
If a buffer is not present, then a '''_glClear''' directed at that buffer has no effect.
 
 
{{PageErrors}}
 
{{KW|_GL_INVALID_VALUE}} is generated if any bit other than the three defined bits is set in {{Parameter|mask}}.
 
 
{{PageUseWith}}
 
{{KW|_glGet}} with argument {{KW|_GL_DEPTH_CLEAR_VALUE}}
 
{{KW|_glGet}} with argument {{KW|_GL_COLOR_CLEAR_VALUE}}
 
{{KW|_glGet}} with argument {{KW|_GL_STENCIL_CLEAR_VALUE}}




{{PageSeeAlso}}
{{PageSeeAlso}}
* [[_GL]]  
* [[_GL|SUB _GL]]
* [[_glClearBuffer]], [[_glClearColor]], [[_glClearDepth]], [[_glClearStencil]]  
* [[_glClearAccum]], [[_glClearColor]], [[_glClearDepth]], [[_glClearIndex]]
* [[_glColorMask]], [[_glDepthMask]], [[_glStencilMask]]
* [[_glClearStencil]], [[_glDrawBuffer]], [https://learn.microsoft.com/en-us/windows/win32/opengl/glgetbooleanv--glgetdoublev--glgetfloatv--glgetintegerv _glGet], [[_glScissor]]
* [[_glDrawBuffer]], [[_glDrawBuffers]]
* [[_glScissor]]




{{PageCopyright}}
{{PageNavigation}}

Latest revision as of 00:36, 28 January 2023

The _glClear statement clears buffers to preset values.


Syntax

_glClear GLbitfield mask


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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