fglDrawPixels(3G)
fglDrawPixels - write a block of pixels to the frame buffer
As shipped in IRIX 6.5.7. Unchanged since IRIX 6.5.
NAME fglDrawPixels - write a block of pixels to the frame buffer FORTRAN SPECIFICATION SUBROUTINE fglDrawPixels( INTEGER*4 width, INTEGER*4 height, INTEGER*4 format, INTEGER*4 type, CHARACTER*8 pixels ) PARAMETERS width, height Specify the dimensions of the pixel rectangle that will be written into the frame buffer. format Specifies the format of the pixel data. Symbolic constants GL_COLOR_INDEX, GL_STENCIL_INDEX, GL_DEPTH_COMPONENT, GL_RGBA, GL_ABGR_EXT, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_LUMINANCE, GL_LUMINANCE_ALPHA and GL_YCRCB_422_SGIX are accepted. type Specifies the data type for pixels. Symbolic constants GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2_EXT, GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT, GL_UNSIGNED_INT_8_8_8_8_EXT, and GL_UNSIGNED_INT_10_10_10_2_EXT are accepted. pixels Specifies a pointer to the pixel data. DESCRIPTION fglDrawPixels reads pixel data from memory and writes it into the frame buffer relative to the current raster position. Use fglRasterPos to set the current raster position, and use fglGet with argument GL_CURRENT_RASTER_POSITION 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 the commands fglPixelStore, fglPixelTransfer, fglPixelMap, and fglPixelZoom. The state of GL_INTERLACE_SGIX (controlled by fglEnable and fglDisable) and the state for the EXT_convolution, SGI_color_matrix, EXT_histogram, and SGI_color_table extensions (see the reference pages for fglPixelTransfer, fglConvolutionFilter2DEXT, fglColorTableSGI, fglHistogramEXT, and fglMinmaxEXT) also affect the results of fglDrawPixels. This reference page describes the effects on fglDrawPixels of some, but not all, of these parameters. type specifies the data type for pixels. The following table summarizes the meaning of the valid constants for type: type corresponding type _______________________________________________________________________ GL_UNSIGNED_BYTE unsigned 8-bit integer GL_BYTE signed 8-bit integer GL_BITMAP single bits in unsigned 8-bit integers GL_UNSIGNED_SHORT unsigned 16-bit integer GL_SHORT signed 16-bit integer GL_UNSIGNED_INT unsigned 32-bit integer GL_INT 32-bit integer GL_FLOAT single-precision floating-point GL_UNSIGNED_BYTE_3_3_2_EXT unsigned 8-bit integer GL_UNSIGNED_SHORT_4_4_4_4_EXT unsigned 16-bit integer GL_UNSIGNED_SHORT_5_5_5_1_EXT unsigned 16-bit integer GL_UNSIGNED_INT_8_8_8_8_EXT unsigned 32-bit integer GL_UNSIGNED_INT_10_10_10_2_EXT unsigned 32-bit integer If type is GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, or GL_FLOAT, then data is read as a sequence of signed or unsigned bytes, shorts, or integers, or single-precision floating-point values. Each of these bytes, shorts, integers, or floating-point values is interpreted as one color component, one depth component, or one index, depending on format. Indices are always treated individually. Colors are treated as groups of one, two, three, or four elements, again based on format. Both individual indices and groups of components are referred to as pixels. If type is GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_INT_8_8_8_8, or GL_UNSIGNED_INT_10_10_10_2 then all the elements of each group are read from a single unsigned byte, unsigned short, or unsigned int. The number of elements per packed pixel is fixed by type, and must match the number of elements per group indicated by format. The following table shows which values of format are valid for each of the packed pixel types: type number elements format ______________________________________________________________________ GL_UNSIGNED_BYTE_3_3_2_EXT 3 GL_RGB GL_UNSIGNED_SHORT_4_4_4_4_EXT 4 GL_RGBA,GL_ABGR_EXT GL_UNSIGNED_SHORT_5_5_5_1_EXT 4 GL_RGBA,GL_ABGR_EXT GL_UNSIGNED_INT_8_8_8_8_EXT 4 GL_RGBA,GL_ABGR_EXT GL_UNSIGNED_INT_10_10_10_2_EXT 4 GL_RGBA,GL_ABGR_EXT The elements in a packed pixel are ordered such that the first element is in the most significant bits, followed by the second element, etc. For example, if type is set to GL_UNSIGNED_SHORT_4_4_4_4_EXT then element 1 is read from bits 15-12, element 2 is read from bits 11-8, element 3 is read from bits 7-4 and element 4 is read from bits 3-0. The assignment of elements to fields in the packed pixel is as described in the table below: format element 1 element 2 element 3 element 4 ___________________________________________________________ GL_RGB red green blue GL_RGBA red green blue alpha GL_ABGR_EXT alpha blue green red If type is GL_BITMAP, the data must be unsigned bytes, and format must be either GL_COLOR_INDEX or GL_STENCIL_INDEX. Each unsigned byte is treated as eight 1-bit pixels, with bit ordering determined by GL_UNPACK_LSB_FIRST. If GL_UNPACK_LSB_FIRST is enabled then the 8 single-bit elements are ordered from most significant to least significant; otherwise the ordering is from least significant to most significant. (see fglPixelStore). If GL_UNPACK_SWAP_BYTES is enabled (see fglPixelStore), byte swapping is performed as the data is read from memory. For pixels that aren't packed, the byte ordering for multibyte color components, depth components, color indices, or stencil indices is reversed. That is, if a four-byte component is made up of bytes b0, b1, b2, b3, it is taken from memory as b3, b2, b1, b0. In the case of the packed pixel types, byte swapping is performed before the elements are extracted from each pixel. width*height pixels are read from memory, starting at location pixels. By default, these pixels are taken from adjacent memory locations, except that after all width pixels are read, the read pointer is advanced to the next four-byte boundary. The four-byte row alignment is specified by fglPixelStore with argument GL_UNPACK_ALIGNMENT, 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 width pixels are read. Refer to the fglPixelStore reference page for details on these options. The width*height pixels that are read from memory are each operated on in the same way, based on the values of several parameters specified by fglPixelTransfer and fglPixelMap. 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 format. These operations generate various fragment values as described below for each format. The number of fragments generated for each source pixel and the assignment of x and y window coordinates to these fragments are common to all formats and are as follows. If the current raster position is invalid, no fragments are generated for any of the source pixels. Else, let (x , y ) be the current raster r r position, and let n and m be the column and row of the source pixel, respectively. For each source pixel, fragments with values computed according to that pixel are generated for destination pixels whose centers are in the rectangle with corners at (x + n * zoom , y + m * interlace * zoom ) and r x r y (x + (n + 1) * zoom , y + (m * interlace + 1) * zoom ). zoom and r x r y x zoom are the values of GL_ZOOM_X and GL_ZOOM_Y, respectively, and y interlace is 1 or 2 depending on whether GL_INTERLACE_SGIX is GL_FALSE or GL_TRUE, respectively. GL_ZOOM_X and GL_ZOOM_Y, initially set to 1.0, are set using fglPixelZoom; GL_INTERLACE_SGIX, initially disabled, is controlled by fglEnable and fglDisable. See the NOTES section for additional discussion of GL_INTERLACE_SGIX. Except for when format is GL_STENCIL_INDEX the generated fragments are 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. For GL_STENCIL_INDEX only the pixel ownership test, the scissor test, and the stencil writemask affect the writes to the stencil buffer. format can assume the following symbolic values: GL_COLOR_INDEX 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 zero. Bitmap data convert to either 0.0 or 1.0. Each fixed-point index is then shifted left by GL_INDEX_SHIFT bits and added to GL_INDEX_OFFSET. If GL_INDEX_SHIFT 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 using the GL_PIXEL_MAP_I_TO_R, GL_PIXEL_MAP_I_TO_G, GL_PIXEL_MAP_I_TO_B, and GL_PIXEL_MAP_I_TO_A tables. If the GL is in color index mode, and if GL_MAP_COLOR is true, the index is replaced with the value that it references in lookup table GL_PIXEL_MAP_I_TO_I. Whether the lookup replacement of the index is b done or not, the integer part of the index is then ANDed with 2 -1, where b is the number of bits in a color index buffer. The resulting index or RGBA color components, and the current raster position z and texture coordinates are assigned to each of the fragments generated for the source pixel. GL_STENCIL_INDEX 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 zero. Bitmap data convert to either 0.0 or 1.0. Each fixed-point index is then shifted left by GL_INDEX_SHIFT bits, and added to GL_INDEX_OFFSET. If GL_INDEX_SHIFT is negative, the shift is to the right. In either case, zero bits fill otherwise unspecified bit locations in the result. If GL_MAP_STENCIL is true, the index is replaced with the value that it references in lookup table GL_PIXEL_MAP_S_TO_S. Whether the lookup replacement of the index is done or not, the integer part of the index is then ANDed b with 2 -1, where b is the number of bits in the stencil buffer. The resulting stencil value is assigned to each of the fragments generated for the source pixel. GL_DEPTH_COMPONENT 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 zero maps to 0.0. The resulting floating-point depth value is then multiplied by GL_DEPTH_SCALE and added to GL_DEPTH_BIAS. The result is clamped to the range [0,1]. The resulting depth component, and the current raster position color or color index and texture coordinates are assigned to each of the fragments generated for the source pixel. GL_RGBA GL_ABGR_EXT Each pixel is a four-component group; for GL_RGBA, the red component is first, followed by green, followed by blue, followed by alpha; for GL_ABGR_EXT the order is alpha, blue, green, and then red. 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. Unsigned integer data is mapped similarly: the largest integer value maps to 1.0, and zero maps to 0.0. The resulting floating-point color values are then multiplied by GL_c_SCALE and added to GL_c_BIAS, where c is RED, GREEN, BLUE, or ALPHA for the respective color components. The results are clamped to the range [0,1]. If GL_MAP_COLOR is true, each color component is scaled by the size of lookup table GL_PIXEL_MAP_c_TO_c, then replaced by the value that it references in that table. c is R, G, B, or A, respectively. The resulting RGBA color components, and the current raster position z and texture coordinates are assigned to each of the fragments generated for the source pixel. GL_RGBA may be faster or slower than GL_ABGR_EXT on a given platform depending on the internal representation of the colors. GL_RED Each pixel is a single red component. This component is converted to the internal floating-point format in the same way as the red component of an RGBA pixel is, then it is converted to an RGBA pixel with green and blue set to 0.0, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_GREEN Each pixel is a single green component. This component is converted to the internal floating-point format in the same way as the green component of an RGBA pixel is, then it is converted to an RGBA pixel with red and blue set to 0.0, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_BLUE Each pixel is a single blue component. This component is converted to the internal floating-point format in the same way as the blue component of an RGBA pixel is, then it is converted to an RGBA pixel with red and green set to 0.0, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_ALPHA Each pixel is a single alpha component. This component is converted to the internal floating-point format in the same way as the alpha component of an RGBA pixel is, then it is converted to an RGBA pixel with red, green, and blue set to 0.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_RGB Each pixel is a three-component group: red first, followed by green, followed by blue. Each component is converted to the internal floating-point format in the same way as the red, green, and blue components of an RGBA pixel are. The color triple is converted to an RGBA pixel with alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_LUMINANCE Each pixel is a single luminance component. This component is converted to the internal floating-point format in the same way as the red component of an RGBA pixel is, then it is converted to an RGBA pixel with red, green, and blue set to the converted luminance value, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_LUMINANCE_ALPHA Each pixel is a two-component group: luminance first, followed by alpha. The two components are converted to the internal floating- point format in the same way as the red component of an RGBA pixel is, then they are converted to an RGBA pixel with red, green, and blue set to the converted luminance value, and alpha set to the converted alpha value. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. GL_YCRCB_422_SGIX Each pixel is a two-component group: chroma first, followed by luminance. The two components are converted to the internal floating-point format of the red, green, and blue components of an RGBA pixel using an unspecified conversion algorithm, and the alpha component of the pixel is set to 1.0. The chroma component of each even-count group in a row represents the Cb chroma value for a pixel pair. The chroma component of each odd-count group in a row represents the Cr chroma value for a pixel pair. Rows of odd length will produce undefined red, green, and blue values for the final pixel in a row. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel. NOTES Enabling GL_INTERLACE_SGIX is equivalent to having a source rectangle with image height equal to 2 * height where every other row contains "transparent" pixels that do not affect the corresponding destination pixels in the frame buffer. For example: fglEnable(GL_INTERLACE_SGIX); set current raster position to (x y ) r, r fglDrawPixels(width, height, GL_RGBA, GL_UNSIGNED_BYTE, I ); 0 set raster position to (x y +zoom ) r, r y fglDrawPixels(width, height, GL_RGBA, GL_UNSIGNED_BYTE, I ); 1 is equivalent to fglDisable( GL_INTERLACE_SGIX); set current raster position to (x y ) r, r fglDrawPixels(width, 2 * height, GL_RGBA, GL_UNSIGNED_BYTE, I ); 2 where pixel rows (0,2,4,...) of I are from image I , and rows 2 0 (1,3,5,...) are from image I . 1 If type is set to GL_UNSIGNED_BYTE_3_3_2_EXT, GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT, GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT and the EXT_packed_pixels extension is not supported then a GL_INVALID_ENUM error is generated. ERRORS GL_INVALID_VALUE is generated if either width or height is negative. GL_INVALID_ENUM is generated if format or type is not one of the accepted values. GL_INVALID_OPERATION is generated if type is set to GL_UNSIGNED_BYTE_3_3_2_EXT, GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT, GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT and the number of elements indicated by type does not match the number indicated by format. GL_INVALID_OPERATION is generated if format is GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_ABGR_EXT, GL_LUMINANCE, GL_LUMINANCE_ALPHA, or GL_YCRCB_422_SGIX, and the GL is in color index mode. GL_INVALID_ENUM is generated if type is GL_BITMAP and format is not either GL_COLOR_INDEX or GL_STENCIL_INDEX. GL_INVALID_OPERATION is generated if format is GL_STENCIL_INDEX and there is no stencil buffer. GL_INVALID_OPERATION is generated if format is GL_DEPTH_COMPONENT and there is no depth buffer. GL_INVALID_OPERATION is generated if fglDrawPixels is executed between the execution of fglBegin and the corresponding execution of fglEnd. ASSOCIATED GETS fglGet with argument GL_CURRENT_RASTER_POSITION fglGet with argument GL_CURRENT_RASTER_POSITION_VALID fglGet with argument GL_INTERLACE_SGIX MACHINE DEPENDENCIES On RealityEngine, RealityEngine2, and VTX systems convolution may not be used in the following circumstances: 1. When rendering to pixmaps. 2. When fragment processing (texturing, depth buffering, alpha testing, multisampling, fog) is enabled. 3. When histogramming or minmax is enabled. 4. When either of the pixel zoom factors has a value other than 1.0 or -1.0. In these cases, fglDrawPixels and fglCopyPixels report a GL_INVALID_OPERATION error and do not transfer any pixels. Performance note for RealityEngine, RealityEngine2, and VTX systems: Unsigned color types use the fastest pixel-drawing path. Smaller types (e.g., GL_UNSIGNED_BYTE) require less host-to-graphics bandwidth, and are therefore faster than larger types (e.g., GL_UNSIGNED_INT). Signed and float types use the significantly slower floating-point pixel-drawing path. The slower pixel-drawing path is also used when the format is GL_DEPTH_COMPONENT and when fragment operations (i.e., depth or alpha testing, texturing, fog, etc.) are enabled. For best performance on XS, XZ, Elan, and Extreme systems set type to GL_UNSIGNED_BYTE and, when drawing to the color buffer, set format to GL_ABGR_EXT. On InfiniteReality systems, signed color-index pixels written to drawables with dual-personality (luminance + color-index) visuals will be sign-extended into the high-order bits of the framebuffer. For example, writing a signed byte value of 0x88 would yield 0xF88 in a 12-bit drawable. The SGIX_ycrcb extension is supported only on O2 systems. The SGIX_interlace extension is supported only on InfiniteReality systems, on RealityEngine, RealityEngine2, and VTX systems, and on O2 systems. The EXT_packed_pixels extension is not supported on RealityEngine, RealityEngine2, and VTX systems. SEE ALSO fglAlphaFunc, fglBlendFunc, fglColorTableSGI, fglCopyPixels, fglConvolutionFilter2DEXT, fglDepthFunc, fglEnable, fglHistogramEXT, fglLogicOp, fglMinmaxEXT, fglPixelMap, fglPixelStore, fglPixelTransfer, fglPixelZoom, fglRasterPos, fglReadPixels, fglScissor, fglSeparableFilter2DEXT, fglStencilFunc.