📄 drawpixels.html
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<HTML><BODY><PRE> <STRONG>NAME</STRONG> <STRONG>glDrawPixels</STRONG> - write a block of pixels to the frame buffer <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG> void <STRONG>glDrawPixels</STRONG>( GLsizei <EM>width</EM>, GLsizei <EM>height</EM>, GLenum <EM>format</EM>, GLenum <EM>type</EM>, const GLvoid *<EM>pixels</EM> ) <STRONG>PARAMETERS</STRONG> <EM>width</EM>, <EM>height</EM> Specify the dimensions of the pixel rectangle to be written into the frame buffer. <EM>format</EM> Specifies the format of the pixel data. Symbolic constants <STRONG>GL_COLOR_INDEX</STRONG>, <STRONG>GL_STENCIL_INDEX</STRONG>, <STRONG>GL_DEPTH_COMPONENT</STRONG>, <STRONG>GL_RGBA</STRONG>, <STRONG>GL_RED</STRONG>, <STRONG>GL_GREEN</STRONG>, <STRONG>GL_BLUE</STRONG>, <STRONG>GL_ALPHA</STRONG>, <STRONG>GL_RGB</STRONG>, <STRONG>GL_LUMINANCE</STRONG>, and <STRONG>GL_LUMINANCE_ALPHA</STRONG> are accepted. <EM>type</EM> Specifies the data type for <EM>pixels</EM>. Symbolic constants <STRONG>GL_UNSIGNED_BYTE</STRONG>, <STRONG>GL_BYTE</STRONG>, <STRONG>GL_BITMAP</STRONG>, <STRONG>GL_UNSIGNED_SHORT</STRONG>, <STRONG>GL_SHORT</STRONG>, <STRONG>GL_UNSIGNED_INT</STRONG>, <STRONG>GL_INT</STRONG>, and <STRONG>GL_FLOAT</STRONG> are accepted. <EM>pixels</EM> Specifies a pointer to the pixel data. <STRONG>DESCRIPTION</STRONG> <STRONG>glDrawPixels</STRONG> reads pixel data from memory and writes it into the frame buffer relative to the current raster position. Use <STRONG>glRasterPos</STRONG> to set the current raster position; use <STRONG>glGet</STRONG> with argument <STRONG>GL_CURRENT_RASTER_POSITION</STRONG> to query the raster position. Several parameters define the encoding of pixel data in memory and control the processing of the pixel data before it is placed in the frame buffer. These parameters are set with four commands: <STRONG>glPixelStore</STRONG>, <STRONG>glPixelTransfer</STRONG>, <STRONG>glPixelMap</STRONG>, and <STRONG>glPixelZoom</STRONG>. This reference page describes the effects on <STRONG>glDrawPixels</STRONG> of many, but not all, of the parameters specified by these four commands. Data is read from <EM>pixels</EM> as a sequence of signed or unsigned bytes, signed or unsigned shorts, signed or unsigned integers, or single-precision floating-point values, depending on <EM>type</EM>. Each of these bytes, shorts, integers, or floating-point values is interpreted as one color or depth component, or one index, depending on <EM>format</EM>. Indices are always treated individually. Color components are treated as groups of one, two, three, or four values, again based on <EM>format</EM>. Both individual indices and groups of components are referred to as pixels. If <EM>type</EM> is <STRONG>GL_BITMAP</STRONG>, the data must be unsigned bytes, and <EM>format</EM> must be either <STRONG>GL_COLOR_INDEX</STRONG> or <STRONG>GL_STENCIL_INDEX</STRONG>. Each unsigned byte is treated as eight 1-bit pixels, with bit ordering determined by <STRONG>GL_UNPACK_LSB_FIRST</STRONG> (see <STRONG>glPixelStore</STRONG>). <EM>width</EM>x<EM>height</EM> pixels are read from memory, starting at location <EM>pixels</EM>. By default, these pixels are taken from adjacent memory locations, except that after all <EM>width</EM> pixels are read, the read pointer is advanced to the next four-byte boundary. The four-byte row alignment is specified by <STRONG>glPixelStore</STRONG> with argument <STRONG>GL_UNPACK_ALIGNMENT</STRONG>, and it can be set to one, two, four, or eight bytes. Other pixel store parameters specify different read pointer advancements, both before the first pixel is read and after all <EM>width</EM> pixels are read. See the <STRONG>glPixelStore</STRONG> reference page for details on these options. The <EM>width</EM>x<EM>height</EM> pixels that are read from memory are each operated on in the same way, based on the values of several parameters specified by <STRONG>glPixelTransfer</STRONG> and <STRONG>glPixelMap</STRONG>. The details of these operations, as well as the target buffer into which the pixels are drawn, are specific to the format of the pixels, as specified by <EM>format</EM>. <EM>format</EM> can assume one of eleven symbolic values: <STRONG>GL_COLOR_INDEX</STRONG> Each pixel is a single value, a color index. It is converted to fixed-point format, with an unspecified number of bits to the right of the binary point, regardless of the memory data type. Floating-point values convert to true fixed-point values. Signed and unsigned integer data is converted with all fraction bits set to 0. Bitmap data convert to either 0 or 1. Each fixed-point index is then shifted left by <STRONG>GL_INDEX_SHIFT</STRONG> bits and added to <STRONG>GL_INDEX_OFFSET</STRONG>. If <STRONG>GL_INDEX_SHIFT</STRONG> is negative, the shift is to the right. In either case, zero bits fill otherwise unspecified bit locations in the result. If the GL is in RGBA mode, the resulting index is converted to an RGBA pixel with the help of the <STRONG>GL_PIXEL_MAP_I_TO_R</STRONG>, <STRONG>GL_PIXEL_MAP_I_TO_G</STRONG>, <STRONG>GL_PIXEL_MAP_I_TO_B</STRONG>, and <STRONG>GL_PIXEL_MAP_I_TO_A</STRONG> tables. If the GL is in color index mode, and if <STRONG>GL_MAP_COLOR</STRONG> is true, the index is replaced with the value that it references in lookup table <STRONG>GL_PIXEL_MAP_I_TO_I</STRONG>. Whether the lookup replacement of the index is done or not, the integer part of the index is then ANDed with 2b-1, where b is the number of bits in a color index buffer. The GL then converts the resulting indices or RGBA colors to fragments by attaching the current raster position <EM>z</EM> coordinate and texture coordinates to each pixel, then assigning x and y window coordinates to the nth fragment such that x = x + n mod width n r y = y + | n/width | n r where (x ,y ) is the current raster position. These pi<STRONG>x</STRONG>elrfragments are then treated just like the fragments generated by rasterizing points, lines, or polygons. Texture mapping, fog, and all the fragment operations are applied before the fragments are written to the frame buffer. <STRONG>GL_STENCIL_INDEX</STRONG> Each pixel is a single value, a stencil index. It is converted to fixed-point format, with an unspecified number of bits to the right of the binary point, regardless of the memory data type. Floating-point values convert to true fixed-point values. Signed and unsigned integer data is converted with all fraction bits set to 0. Bitmap data convert to either 0 or 1. Each fixed-point index is then shifted left by <STRONG>GL_INDEX_SHIFT</STRONG> bits, and added to <STRONG>GL_INDEX_OFFSET</STRONG>. If <STRONG>GL_INDEX_SHIFT</STRONG> is negative, the shift is to the right. In either case, zero bits fill otherwise unspecified bit locations in the result. If <STRONG>GL_MAP_STENCIL</STRONG> is true, the index is replaced with the value that it references in lookup table <STRONG>GL_PIXEL_MAP_S_TO_S</STRONG>. Whether the lookup replacement of the index is done or not, the integer part of the index is then ANDed with 2b-1, where b is the number of bits in the stencil buffer. The resulting stencil indices are then written to the stencil buffer such that the nth index is written to location x = x + n mod width n r y = y + | n/width | where (x ,y ) is the current raster position. Only the pixel ow<STRONG>n</STRONG>er<STRONG>s</STRONG>hip test, the scissor test, and the stencil writemask affect these write operations. <STRONG>GL_DEPTH_COMPONENT</STRONG> Each pixel is a single-depth component. Floating-point data is converted directly to an internal floating- point format with unspecified precision. Signed integer data is mapped linearly to the internal floating-point format such that the most positive representable integer value maps to 1.0, and the most negative representable value maps to -1.0. Unsigned integer data is mapped similarly: the largest integer value maps to 1.0, and 0 maps to 0.0. The resulting floating-point depth value is then multiplied by by <STRONG>GL_DEPTH_SCALE</STRONG> and added to <STRONG>GL_DEPTH_BIAS</STRONG>. The result is clamped to the range [0,1]. The GL then converts the resulting depth components to fragments by attaching the current raster position color or color index and texture coordinates to each pixel, then assigning x and y window coordinates to the nth fragment such that x = x + n mod width n r y = y + | n/width | n r where (x ,y ) is the current raster position. These pixel fr<STRONG>a</STRONG>gm<STRONG>e</STRONG>nts are then treated just like the fragments generated by rasterizing points, lines, or polygons. Texture mapping, fog, and all the fragment operations are applied before the fragments are written to the frame buffer. <STRONG>GL_RGBA</STRONG> Each pixel is a four-component group: for <STRONG>GL_RGBA</STRONG>, the red component is first, followed by green, followed by blue, followed by alpha. Floating-point values are converted directly to an internal floating-point format with unspecified precision. Signed integer values are mapped linearly to the internal floating-point format such that the most positive representable integer value maps to 1.0, and the most negative representable value maps to -1.0. (Note that this mapping does not convert 0 precisely to 0.0.) Unsigned integer data is mapped similarly: the largest integer value maps to 1.0, and 0 maps to 0.0. The resulting floating-point color values are then multiplied by <STRONG>GL_c_SCALE</STRONG> and added to <STRONG>GL_c_BIAS</STRONG>, where <EM>c</EM> is RED, GREEN, BLUE, and ALPHA for the respective color components. The results are clamped to the range [0,1].⌨️ 快捷键说明
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