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Active Forums => Programs => Topic started by: Ashish on June 18, 2018, 05:30:30 am

Title: OpenGL Context Capture Demo
Post by: Ashish on June 18, 2018, 05:30:30 am
Hi everyone!
Now finally, it is possible to make OpenGL frame retain on screen.
The program code below does this -

Controls -  Press Space to capture OpenGL context and 'c' to clear software screen.


Code: QB64: [Select]
  1. 'OpenGL context capture example
  2. 'by Ashish Kushwaha
  3.  
  4. _TITLE "Hit *Space* to capture GL context and 'c' to clear software screen"
  5. SCREEN _NEWIMAGE(600, 600, 32)
  6.  
  7. DIM SHARED glAllow AS _BYTE
  8. DIM SHARED GL_Color_Buffer~%%(_WIDTH * _HEIGHT * 3)
  9. DIM SHARED keyHit AS LONG
  10.  
  11. DIM SHARED GL_Context&, buffer_done
  12. buffer_done = 0
  13. 'CLS
  15. glAllow = -1
  17.     keyHit = _KEYHIT
  18.     IF keyHit = ASC("c") THEN CLS , 1
  19.     IF buffer_done THEN
  20.         _CLEARCOLOR _RGB(0, 0, 0), GL_Context&
  21.         _PUTIMAGE , GL_Context&
  22.         _FREEIMAGE GL_Context&
  23.         buffer_done = 0
  24.     END IF
  25.     _DISPLAY
  26.     _LIMIT 30
  28.  
  29.  
  30. SUB _GL ()
  31.     STATIC fps AS LONG
  32.     IF NOT glAllow THEN EXIT SUB
  33.  
  34.     '_glDisable _GL_MULTISAMPLE <<<< uncomment this line if you are using latest (06/18/2018) build of QB64.
  35.  
  37.  
  38.     _glClearColor 0, 0, 0, 1
  39.     _glClear _GL_COLOR_BUFFER_BIT
  40.  
  41.     _glMatrixMode _GL_MODELVIEW
  43.  
  44.     _glRotatef fps, 0, 0, 1
  45.  
  46.     _glBegin _GL_TRIANGLES
  47.  
  48.     _glColor3f 1, 0, 0
  49.     _glVertex2f 0, 1
  50.     _glColor3f 0, 1, 0
  51.     _glVertex2f -1, -1
  52.     _glColor3f 0, 0, 1
  53.     _glVertex2f 1, -1
  54.     _glEnd
  55.  
  56.     IF keyHit = ASC(" ") AND NOT buffer_done THEN GL_Context& = getOpenGLContextImage: buffer_done = 1
  57.  
  58.     _glFlush
  59.  
  60.     fps = fps + 1
  62.  
  63. FUNCTION getOpenGLContextImage& ()
  64.     'storing GL Color Buffer in our  GL_Color_Buffer() array
  65.     _glReadBuffer _GL_BACK
  66.     _glPixelStorei _GL_UNPACK_ALIGNMENT, 1
  67.     _glReadPixels 0, 0, _WIDTH, _HEIGHT, _GL_RGB, _GL_UNSIGNED_BYTE, _OFFSET(GL_Color_Buffer~%%())
  68.  
  70.     getOpenGLContextImage& = _NEWIMAGE(_WIDTH, _HEIGHT, 32) 'create an image handle
  71.     DIM m AS _MEM
  72.     m = _MEMIMAGE(getOpenGLContextImage&) 'store it in memory
  73.     i& = 0
  74.     FOR y = _HEIGHT(getOpenGLContextImage&) - 1 TO 0 STEP -1
  75.         FOR x = 0 TO _WIDTH(getOpenGLContextImage&) - 1
  76.             index& = 4 * (x + y * _WIDTH(getOpenGLContextImage&))
  77.             _MEMPUT m, m.OFFSET + index&, GL_Color_Buffer~%%(i& + 2) AS _UNSIGNED _BYTE 'blue
  78.             _MEMPUT m, m.OFFSET + index& + 1, GL_Color_Buffer~%%(i& + 1) AS _UNSIGNED _BYTE 'green
  79.             _MEMPUT m, m.OFFSET + index& + 2, GL_Color_Buffer~%%(i&) AS _UNSIGNED _BYTE 'red
  80.             _MEMPUT m, m.OFFSET + index& + 3, 255 AS _UNSIGNED _BYTE 'alpha
  81.             i& = i& + 3
  82.     NEXT x, y
  83.     _MEMFREE m
  86.  
  87.  
Title: Re: OpenGL Context Capture Demo
Post by: Petr on June 18, 2018, 04:13:39 pm
Thanks for sharing. This is very useful, knowing how to do it.
Title: Re: OpenGL Context Capture Demo
Post by: Ashish on June 19, 2018, 03:43:03 am
Quote from: Petr on June 18, 2018, 04:13:39 pm
Thanks for sharing. This is very useful, knowing how to do it.
I'm glad that it is useful to you. :)
Title: Re: OpenGL Context Capture Demo
Post by: Ashish on June 23, 2018, 11:47:53 am
Here's a fading effect achieved by software screen -
Code: QB64: [Select]
  1. 'OpenGL context capture example
  2. 'by Ashish Kushwaha
  3.  
  4. _TITLE "Rendering OpenGL to software screen"
  5. SCREEN _NEWIMAGE(600, 600, 32)
  6.  
  7. DIM SHARED glAllow AS _BYTE
  8. DIM SHARED GL_Color_Buffer~%%((_WIDTH * _HEIGHT * 4) - 1)
  9. DIM SHARED keyHit AS LONG
  10.  
  11. DIM SHARED GL_Context&, buffer_done
  12.  
  13. buffer_done = 0
  14. 'CLS
  16. glAllow = -1
  18.     keyHit = _KEYHIT
  19.  
  20.     IF buffer_done THEN
  21.         _CLEARCOLOR _RGB(0, 0, 0), GL_Context&
  22.         _PUTIMAGE (0, _HEIGHT - 1)-(_WIDTH - 1, 0), GL_Context& 'flip again the image (opengl returns a vertically fliped image)
  23.         _FREEIMAGE GL_Context&
  24.         buffer_done = 0
  25.     END IF
  26.     LINE (0, 0)-(600, 600), _RGBA(0, 0, 0, 10), BF
  27.     _DISPLAY
  28.     _LIMIT 60
  30.  
  31.  
  32. SUB _GL ()
  33.     STATIC fps AS LONG, tt#
  34.     IF NOT glAllow THEN EXIT SUB
  35.     IF fps = 0 THEN tt# = TIMER
  36.  
  38.  
  39.     _glMatrixMode _GL_MODELVIEW
  41.  
  42.     _glRotatef fps, 0, 0, 1
  43.  
  44.     _glBegin _GL_TRIANGLES
  45.  
  46.     _glColor3f 1, 0, 0
  47.     _glVertex2f 0, 1
  48.     _glColor3f 0, 1, 0
  49.     _glVertex2f -1, -1
  50.     _glColor3f 0, 0, 1
  51.     _glVertex2f 1, -1
  52.     _glEnd
  53.  
  54.  
  55.     IF NOT buffer_done THEN GL_Context& = getOpenGLContextImage: buffer_done = 1
  56.  
  57.     _glFlush
  58.  
  59.     fps = fps + 1
  61.  
  62. FUNCTION getOpenGLContextImage& ()
  63.     'storing GL Color Buffer in our  GL_Color_Buffer() array
  64.     _glReadBuffer _GL_BACK
  65.     _glPixelStorei _GL_UNPACK_ALIGNMENT, 1
  66.     _glReadPixels 0, 0, _WIDTH, _HEIGHT, _GL_BGRA_EXT, _GL_UNSIGNED_BYTE, _OFFSET(GL_Color_Buffer~%%())
  67.  
  69.  
  70.     ' the below one will store vertically flip image
  71.     getOpenGLContextImage& = _NEWIMAGE(_WIDTH, _HEIGHT, 32) 'create an image handle
  72.     DIM m AS _MEM, m2 AS _MEM
  73.  
  74.     m = _MEMIMAGE(getOpenGLContextImage&) 'store it in memory
  75.     m2 = _MEM(GL_Color_Buffer~%%())
  76.  
  77.     _MEMCOPY m2, m2.OFFSET, m2.SIZE TO m, m.OFFSET 'using _MEMCOPY instead of nested loop
  78.     _MEMFREE m
  79.     _MEMFREE m2
  80.  
  83.  
  84.  
Title: Re: OpenGL Context Capture Demo
Post by: FellippeHeitor on November 01, 2020, 07:34:39 am
Old topic but somehow I missed this: great job, Ashish!
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