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To better exercise pixel packing, replace regular glReadPixels with four 

ReadPixels that get the image piece by piece.
This commit is contained in:
Brian Paul 2005-05-18 15:44:13 +00:00
parent 2b2bd08589
commit 8818eae253
1 changed files with 57 additions and 3 deletions
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60
progs/demos/readpix.c
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@ -39,6 +39,10 @@ static GLenum ReadType = GL_UNSIGNED_BYTE;
#endif
#if 0
static GLenum ReadFormat = GL_RGB;
static GLenum ReadType = GL_UNSIGNED_BYTE;
#endif
#if 0
static GLenum ReadFormat = GL_RGB;
static GLenum ReadType = GL_UNSIGNED_SHORT_5_6_5;
#endif
#if 0
@ -96,6 +100,45 @@ SetupPixelTransfer(GLboolean invert)
}
/**
* Exercise Pixel Pack parameters by reading the image in four pieces.
*/
static void
ComplexReadPixels(GLint x, GLint y, GLsizei width, GLsizei height,
GLenum format, GLenum type, GLvoid *pixels)
{
const GLsizei width0 = width / 2;
const GLsizei width1 = width - width0;
const GLsizei height0 = height / 2;
const GLsizei height1 = height - height0;
glPixelStorei(GL_PACK_ROW_LENGTH, width);
/* lower-left quadrant */
glReadPixels(x, y, width0, height0, format, type, pixels);
/* lower-right quadrant */
glPixelStorei(GL_PACK_SKIP_PIXELS, width0);
glReadPixels(x + width0, y, width1, height0, format, type, pixels);
/* upper-left quadrant */
glPixelStorei(GL_PACK_SKIP_PIXELS, 0);
glPixelStorei(GL_PACK_SKIP_ROWS, height0);
glReadPixels(x, y + height0, width0, height1, format, type, pixels);
/* upper-right quadrant */
glPixelStorei(GL_PACK_SKIP_PIXELS, width0);
glPixelStorei(GL_PACK_SKIP_ROWS, height0);
glReadPixels(x + width0, y + height0, width1, height1, format, type, pixels);
/* restore defaults */
glPixelStorei(GL_PACK_SKIP_PIXELS, 0);
glPixelStorei(GL_PACK_SKIP_ROWS, 0);
glPixelStorei(GL_PACK_ROW_LENGTH, ImgWidth);
}
static void
Display( void )
{
@ -111,8 +154,13 @@ Display( void )
glRasterPos2i(APosX, APosY);
glEnable(GL_DITHER);
SetupPixelTransfer(GL_FALSE);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glDrawPixels(ImgWidth, ImgHeight, ImgFormat, GL_UNSIGNED_BYTE, Image);
/* might try alignment=4 here for testing */
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
/* do readpixels, drawpixels */
glRasterPos2i(BPosX, 5);
PrintString("Read/DrawPixels");
@ -138,8 +186,14 @@ Display( void )
else {
/* clear the temporary image to white (helpful for debugging */
memset(TempImage, 255, ImgWidth * ImgHeight * 4);
#if 0
/* you might use this when debugging */
glReadPixels(APosX, APosY, ImgWidth, ImgHeight,
ReadFormat, ReadType, TempImage);
#else
ComplexReadPixels(APosX, APosY, ImgWidth, ImgHeight,
ReadFormat, ReadType, TempImage);
#endif
}
glRasterPos2i(BPosX, BPosY);
glDisable(GL_DITHER);
@ -253,14 +307,14 @@ Init( GLboolean ciMode )
printf("Loaded %d by %d image\n", ImgWidth, ImgHeight );
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glPixelStorei(GL_UNPACK_ROW_LENGTH, ImgWidth);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glPixelStorei(GL_PACK_ROW_LENGTH, ImgWidth);
Reset();
TempImage = (GLubyte *) malloc(ImgWidth * ImgHeight * 4 * sizeof(GLubyte));
/* allocate an extra 1KB in case we're tinkering with pack alignment */
TempImage = (GLubyte *) malloc(ImgWidth * ImgHeight * 4 * sizeof(GLubyte)
+ 1000);
assert(TempImage);
}