[gameprogrammer] Re: GL

["Alan Wolfe" <alan.wolfe@gmail.com>]

Thanks!! (:

On 8/3/07, Husam Zakaria <hzcppff@gmail.com> 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:

Constant	R Bits	G Bits	B Bits	A Bits	L Bits	I 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				4	4
GL_LUMINANCE6_ALPHA2				2	6
GL_LUMINANCE8_ALPHA8				8	8
GL_LUMINANCE12_ALPHA4				4	12
GL_LUMINANCE12_ALPHA12				12	12
GL_LUMINANCE16_ALPHA16				16	16
GL_INTENSITY
GL_INTENSITY4						4
GL_INTENSITY8						8
GL_INTENSITY12						12
GL_INTENSITY16						16
GL_RGB
GL_R3_G3_B2	3	3	2
GL_RGB4	4	4	4
GL_RGB5	5	5	5
GL_RGB8	8	8	8
GL_RGB10	10	10	10
GL_RGB12	12	12	12
GL_RGB16	16	16	16
GL_RGBA
GL_RGBA2	2	2	2	2
GL_RGBA4	4	4	4	4
GL_RGB5_A1	5	5	5	1
GL_RGBA8	8	8	8	8
GL_RGB10_A2	10	10	10	2
GL_RGBA12	12	12	12	12
GL_RGBA16	16	16	16	16

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@gmail.com> 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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