[gameprogrammer] Re: GL

I didn't even know that call existed!! I'm so happy to have learned this on the sly. I was going to suggest setting up a render-to- texture, but this seems MUCH more straightforward! 

-- Scott


On 2007/08/03, at 11:32, Husam Zakaria wrote:
of course you can do that by using glCopyTextImage1D or glCopyTextImage2D
The glCopyTexImage2D function copies pixels from the framebuffer into a two-dimensional texture image. 

void glCopyTexImage2D(
GLenum target,
GLint level,
GLenum internalFormat,
GLint x,
GLint y,
GLsizei width,
GLsizei height,
GLint border
); Parameters target The target to which the image data will be changed. Must have the value GL_TEXTURE_2D. level The level-of- detail number. Level 0 is the base image. Level n is the nth mipmap reduction image. internalFormat The internal format and resolution of the texture data. The values 1, 2, 3, and 4 are not accepted for internalFormat. The parameter can assume one of the following symbolic values: 
ConstantR BitsG BitsB BitsA BitsL BitsI Bits
GL_ALPHA





GL_ALPHA4


4

GL_ALPHA8


8

GL_ALPHA12


12

GL_ALPHA16


16

GL_LUMINANCE





GL_LUMINANCE4



4
GL_LUMINANCE8



8
GL_LUMINANCE12



12
GL_LUMINANCE16



16
GL_LUMINANCE_ALPHA





GL_LUMINANCE4_ALPHA4


44
GL_LUMINANCE6_ALPHA2


26
GL_LUMINANCE8_ALPHA8


88
GL_LUMINANCE12_ALPHA4


412
GL_LUMINANCE12_ALPHA12


1212
GL_LUMINANCE16_ALPHA16


1616
GL_INTENSITY





GL_INTENSITY4




4
GL_INTENSITY8




8
GL_INTENSITY12




12
GL_INTENSITY16




16
GL_RGB





GL_R3_G3_B2332


GL_RGB4444


GL_RGB5555


GL_RGB8888


GL_RGB10101010


GL_RGB12121212


GL_RGB16161616


GL_RGBA





GL_RGBA22222

GL_RGBA44444

GL_RGB5_A15551

GL_RGBA88888

GL_RGB10_A21010102

GL_RGBA1212121212

GL_RGBA1616161616
x, y The window coordinates of the lower-left corner of the rectangular region of pixels to be copied. width The width of the texture image. Must be 2n + 2 * border for some integer n. height The height of the texture image. Must be 2n + 2 * border for some integer n. border The width of the border. Must be either zero or 1. Remarks The glCopyTexImage2D function defines a two-dimensional texture image using pixels from the current framebuffer, rather than from main memory as is the case for glTexImage2D.
Using the mipmap level specified with level, texture arrays are defined as a rectangle of pixels with the lower-left corner located at the coordinates x and y, width equal to width + (2 * border), and a height equal to height + (2 * border). The internal format of the texture array is specified with the internalFormat parameter.
The glCopyTexImage2D function processes the pixels in a row in the same way as glCopyPixels except that before the final conversion of the pixels, all pixel component values are clamped to the range [0, 1] and converted to the texture's internal format for storage in the texture array. Pixel ordering is determined with lower x and y coordinates corresponding to lower s and t texture coordinates. If any of the pixels within a specified row of the current framebuffer are outside the window associated with the current rendering context, then their values are undefined. 

You cannot include calls to glCopyTexImage2D in display lists.
Note The glCopyTexImage2D function is only available in OpenGL version 1.1 or later.
Texturing has no effect in color-index mode. The glPixelStore and glPixelTransfer functions affect texture images in exactly the way they affect glDrawPixels.
The following function retrieves information related to glCopyTexImage2D: 

glIsEnabled with argument GL_TEXTURE_2D



On 8/3/07, Alan Wolfe <alan.wolfe@xxxxxxxxx> wrote: Hey guys,

Does anyone know if theres a way to take part of the screen and make a
gl texture out of that?

Basically what i'm trying to do is a post processing effect where i
take whats on the screen and manipulate it.  glreadpixels is going way
slow and i was thinking i only need to take an image from the screen
(video memory) and make a texture with it (more video memory) so is
there a way to do it without having to pull the pixel data into system
memory?

Thanks!!
Alan

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