skia / external / github.com / KhronosGroup / OpenGL-Registry / 940113e244cf1a1a4368393ea1e148f0d096ae61 / . / extensions / SGI / SGI_fft.txt

Name | |

SGI_fft | |

Name Strings | |

GL_SGI_fft | |

Status | |

XXX - Not complete yet!!! | |

Version | |

Last Modified Date: April 24, 2000 | |

Author Revision: $Header: //depot/main/doc/registry/extensions/SGI/fft.spec#11 $ | |

Number | |

99 | |

Dependencies | |

SGI_complex is required | |

SGI_complex_type is required | |

SGI_color_table affects the definition of this extension | |

EXT_convolution affects the definition of this extension | |

Overview | |

The Fast Fourier Transform (FFT) is a set of efficient algorithms for | |

computing the discrete Fourier transform (DFT) that are based on the | |

fundamental principle of decomposing the computation of the Fourier | |

transform of a sequence into successively smaller discrete Fourier | |

transforms. | |

This extension defines complex to complex pixel formats 1-dimensional | |

fast Fourier transforms in the pixel transfer process. Pixel drawing, | |

reading and copying are all candidates for FFTs. Note that it is possible | |

to compute the forward DFT, inverse DFT, multi-dimensional DFT, real to | |

complex DFT, and any combination of the above efficiently, using the complex | |

to complex 1-dimensional forward FFT only. | |

The number of input elements must be a power of two. If the original | |

series size is not a power of two, the data can be padded with zeros or | |

resampled to meet this prerequisite. It is the user's responsibility to | |

satisfy this constraint. | |

FFT precision is implementation dependent. | |

This extension replaces the convolution block of the pixel pipeline | |

with a new pixel transform block. The pixel transform block | |

can be configured to be the convolution operation defined by the | |

EXT_convolution extension or the fft operation defined in this extension. | |

It also can be enabled or disabled all together. | |

Issues | |

* some platforms (i.e Moosehead and MG) may initially only implement 1D and | |

2D FFT's, if this is the case, should we break up the 3D extension as a | |

separate one? Will these machines be forced to say that this extension | |

is not 'fully' supported if they do not implement 3D? | |

resolved: we will only support 1D ffts and allow later | |

expandibility to 2D and 3D. still need to resolve whether we | |

support 1D in row, column, and depth order on 2D and 3D images | |

to make it easier to build 2D and 3D ffts. | |

* We also have to take in account a possible broadening of the restricted | |

list of input sizes of powers of 2, to sizes whos prime factors are 2, 3, | |

and maybe even 5. The motivation is induced by standard video image sizes | |

that are not always powers of 2. The FFT of the zero padded series and | |

the FFT of the original series are not always equivalent | |

resolved: we will only support power of 2 input sizes | |

* 1D FFTs are defined on images of all dimensions. This is different from | |

the way CONVOLUTIONS are defined. We might need a parameter or name that | |

specifies in what dimension does a 1D FFT applied to an incoming n-D | |

image. | |

* we refer to the new pixel processing block which can be configured | |

as either convolution or fft as the pixel transform. Is there a better | |

name for this. | |

* it seems the way the spec is defined, that only way to disable the | |

scale and bias is to select convolve as the transform and use disable | |

the convolve using Disable. Is there a better way? | |

* Even though the algorithm is not described in the spec, this | |

knowledge might have some importance to the user, because | |

precision becomes a more important issue, and the size of the | |

FFT directly supported will typically be limited. In order to | |

provide operators that can be used as basic blocks for computing | |

larger size of FFTs, some extra parameters might be appropriate. | |

This is a low priority issue, as the suggested parameters can be added | |

later, if the need arises. | |

FFT_TYPE_UNKNOWN_SGI | |

FFT_TYPE_RADIX4_DIF_NIO_SGI | |

FFT_TYPE_RADIX4_DIT_NOO_SGI | |

DIF - Decimation in Frequency | |

DIT - Decimation in Time | |

NIO - Normal Input Order | |

NOO - Normal Output Order | |

The FFT_SORT_SGI parameter can be used to suppress sorting into digit | |

reverse order. | |

* The TRANSPOSE_SGI parameter can be used to transpose a 2-D image after | |

performing 1-D fft on the image rows before it is placed at the | |

destination color buffer, in order to expedite the 2-D fft. | |

HP has already an extension in effect, I'm told, that does those kind of | |

operations on images. It make sense to place it immediately before the | |

zoom operation. | |

New Procedures and Functions | |

void PixelTransformSGI(enum target); | |

void PixelTransformParameterfSGI(enum target, | |

enum pname, | |

float param); | |

void PixelTransformParameterfvSGI(enum target, | |

enum pname, | |

const float* params); | |

void PixelTransformParameteriSGI(enum target, | |

enum pname, | |

int param); | |

void PixelTransformParameterivSGI(enum target, | |

enum pname, | |

const int* params); | |

void GetPixelTransformParameterfvSGI(enum target, | |

enum pname, | |

float* params); | |

void GetPixelTransformParameterivSGI(enum target, | |

enum pname, | |

int* params); | |

New Tokens | |

Accepted by the <target> parameter of PixelTransformSGI: | |

CONVOLUTION_SGI 0x81C5 | |

FFT_1D_SGI 0x81C6 | |

Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, | |

and GetDoublev: | |

PIXEL_TRANSFORM_OPERATOR_SGI 0x81C4 | |

Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, | |

and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, | |

and GetDoublev: | |

PIXEL_TRANSFORM_SGI 0x81C7 | |

Accepted by the <pname> parameter of GetPixelTransformParameterfvSGI | |

and GetPixelTransformParameterivSGI: | |

MAX_FFT_WIDTH_SGI 0x81C8 | |

Accepted by the <pname> parameter of PixelTransferi, PixelTransferf, | |

and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, | |

and GetDoublev: | |

POST_TRANSFORM_RED_SCALE_SGI ???? | |

POST_TRANSFORM_GREEN_SCALE_SGI ???? | |

POST_TRANSFORM_BLUE_SCALE_SGI ???? | |

POST_TRANSFORM_ALPHA_SCALE_SGI ???? | |

POST_TRANSFORM_RED_BIAS_SGI ???? | |

POST_TRANSFORM_GREEN_BIAS_SGI ???? | |

POST_TRANSFORM_BLUE_BIAS_SGI ???? | |

POST_TRANSFORM_ALPHA_BIAS_SGI ???? | |

*Note* - values defined in the spec, but not documented below | |

SORT_SGI = 0x81C9 | |

TRANSPOSE_SGI = 0x81CA | |

Additions to Chapter 2 of the OpenGL Specification (OpenGL Operation) | |

None | |

Additions to Chapter 3 of the OpenGL Specification (Rasterization) | |

The specification of pixel operators is added to the GL Specification in | |

section 3.6.2, "Pixel Transfer Modes." | |

The operations of the pixel transforms are added to the GL Specification in | |

section 3.6.3, "Rasterization of Pixel Rectangles, immediately following the | |

subsection "Index Lookup", and immediately prior to the operations described | |

by EXT_histogram. Transforms are enabled, disabled, and queried by calling | |

Enable, Disable and IsEnabled respectively. The pixel transform is enabled | |

by default. A particular transform is selected by calling PixelTransformSGI | |

with the <target> parameter set to one of: CONVOLUTION_SGI, or FFT_1D_SGI. | |

The pixel transform is performed only for RGBA groups, though these groups | |

may have been specified as color indexes and converted to RGBA by index | |

table lookup. | |

The convolution transform is described in the EXT_convolution | |

specification. | |

If pixel transform is enabled and FFT_1D_SGI is selected, the 1-dimensional | |

fft is applied to the image passed to TexImage1D, and to 1-dimensional | |

textures queried by GetTexImage. It is applied on a per-row basis to | |

the 2-dimensional images passed to DrawPixels, CopyPixels, ReadPixels, | |

TexImage2D, TexSubImage2DEXT, CopyTexImage2DEXT, CopyTexSubImage2DEXT, | |

and to 2-dimensional images queried by GetTexImage. It is also applied | |

on a per-row basis to the 3-dimensional images passed to CopyTexSubImage3DEXT, | |

TexImage3DEXT, and TexSubImage3DEXT, and to 3-dimensional images queried by | |

GetTexImage. | |

The discrete fourier transform is a complex valued sum of products of | |

source image pixels and the discretely sampled function exp(2PIikn/N). | |

[exp(2PIix) == sin(x)+icos(x)] | |

Source image pixels always have four components: red, green, blue, | |

and alpha. Individual color components of each source image pixel | |

are always independently processed as part of the transform. | |

The discrete fourier transform is defined differently for each of | |

the three transform types. In the following equations the | |

SUM{}{}equation | |

notation indicates the sum of the equation evaluated for all | |

combinations of conditions indicated within the curly brackets. The | |

variables Ws, Hs, and Ds refer to the dimensions of the source | |

pixel image. | |

The discrete fourier transform equation is: | |

1-dimensional transform: | |

C[n] = SUM{k = 0 through Ws-1} | |

Cs[k]*exp(2PIikn/Ws) | |

The inverse transform equation is: | |

1-dimensional transform: | |

C[n] = SUM{k = 0 through Ws-1} | |

Cs[k]*exp(-2PIikn/Ws) | |

----- | |

Ws | |

The particular fft algorithm is left unspecified to allow greater | |

flexibility for implementations. | |

If a pixel transform operation is performed, the resulting image is scaled | |

and biased by parameters specified using the PixelTransfer command. | |

These operations are: | |

red = red * POST_TRANSFORM_RED_SCALE_SGI | |

+ POST_TRANSFORM_RED_BIAS_SGI | |

green = green * POST_TRANSFORM_GREEN_SCALE_SGI | |

+ POST_TRANSFORM_GREEN_BIAS_SGI | |

blue = blue * POST_TRANSFORM_BLUE_SCALE_SGI | |

+ POST_TRANSFORM_BLUE_BIAS_SGI | |

alpha = alpha * POST_TRANSFORM_ALPHA_SCALE_SGI | |

+ POST_TRANSFORM_ALPHA_BIAS_SGI | |

If no fft operation is performed, the scale and bias are not | |

performed either. | |

Additions to Chapter 4 of the GL Specification (Per-Fragment Operations | |

and the Framebuffer) | |

The operation of fft during pixel copy and query operations is | |

identical to the operation during pixel drawing and texture image | |

definition. | |

Additions to Chapter 5 of the GL Specification (Special Functions) | |

Commands GetPixelTransformParameterfvSGI and | |

GetPixelTransformParameterivSGI are not include in display lists. | |

They are always executed immediately. | |

Additions to Chapter 6 of the GL Specification (State and State Requests) | |

Integer and floating point query functions | |

GetPixelTransformParameterivSGI and | |

GetPixelTransformParameterfvSGI are provided. <target> must be | |

FFT_1D_SGI. <pname> must be MAX_FFT_WIDTH_SGI. The value of the | |

specified parameter is returned in <params>. | |

Additions to the GLX Specification | |

None | |

GLX Protocol | |

None | |

Dependencies on EXT_convolution | |

If EXT_convolution is defined, then the post convolution scale and | |

bias enumerants POST_CONVOLUTION_RED_SCALE_EXT, | |

POST_CONVOLUTION_GREEN_SCALE_EXT, POST_CONVOLUTION_BLUE_SCALE_EXT, | |

POST_CONVOLUTION_ALPHA_SCALE_EXT, POST_CONVOLUTION_RED_BIAS_EXT, | |

POST_CONVOLUTION_GREEN_BIAS_EXT, POST_CONVOLUTION_BLUE_BIAS_EXT, | |

and POST_CONVOLUTION_ALPHA_BIAS_EXT are aliased with the | |

corresponding POST_TRANSFORM scale and biases in the obvious way. | |

The commands ConvolutionParameterfEXT, ConvolutionParameterfvEXT, | |

ConvolutionParameteriEXT, ConvolutionParameterivEXT, | |

GetConvolutionParameterfvEXT, and GetConvolutionParameterivEXT are | |

equivalent to the corresponding PixelTransformParameterfSGI, | |

PixelTransformParameterfvSGI, PixelTransformParameteriSGI, | |

PixelTransformParameterivSGI, GetPixelTransformParameterfvSGI, and | |

GetPixelTransformParameterivSGI commands and should be superseded | |

by the PixelTransform versions of the commands. | |

If EXT_convolution is not defined, then specifying CONVOLUTION_SGI for the | |

<target> parameter to the command PixelTransformSGI will result in an | |

INVALID_OPERATION error. | |

Errors | |

INVALID_ENUM is generated if PixelTransformParameteriSGI, | |

PixelTransformParameterfSGI, PixelTransformParameterivSGI, | |

PixelTransformParameterfvSGI, GetPixelTransformParameterivSGI, or | |

GetPixelTransformParameterfvSGI parameter <target> is not | |

FFT_1D_SGI. | |

INVALID_ENUM is generated if PixelTransformParameteriSGI, | |

PixelTransformParameterfSGI, PixelTransformParameterivSGI, or | |

PixelTransformParameterfvSGI, parameter <target> is GL_FFT_1D_SGI, and | |

parameter <pname> is not TRANSPOSE_SGI. | |

INVALID_ENUM is generated if GetPixelTransformParameterivSGI, | |

or GetPixelTransformParameterfvSGI, parameter <target> is GL_FFT_1D_SGI, and | |

parameter <pname> is not MAX_FFT_WIDTH_SGI or TRANSPOSE_SGI. | |

INVALID_VALUE is generated if the width, <x> specified in DrawPixels, | |

TexImage1D or TexImage2D is less than zero, or greater than | |

MAX_FFT_WIDTH_SGI or not a power or two. | |

INVALID_OPERATION is generated if PixelTransformParameterfSGI, | |

PixelTransformParameterfvSGI, PixelTransformParameteriSGI, | |

PixelTransformParameterivSGI, GetPixelTransformParameterfvSGI, or | |

GetPixelTransformParameterivSGI is executed between execution of | |

Begin and the corresponding execution of End. | |

New State | |

Get Value Get Command Type Initial Value Attribute | |

--------- ----------- ---- ------------- --------- | |

POST_TRANSFORM_RED_SCALE_SGI GetFloatv R 1 pixel | |

POST_TRANSFORM_GREEN_SCALE_SGI GetFloatv R 1 pixel | |

POST_TRANSFORM_BLUE_SCALE_SGI GetFloatv R 1 pixel | |

POST_TRANSFORM_ALPHA_SCALE_SGI GetFloatv R 1 pixel | |

POST_TRANSFORM_RED_BIAS_SGI GetFloatv R 0 pixel | |

POST_TRANSFORM_GREEN_BIAS_SGI GetFloatv R 0 pixel | |

POST_TRANSFORM_BLUE_BIAS_SGI GetFloatv R 0 pixel | |

POST_TRANSFORM_ALPHA_BIAS_SGI GetFloatv R 0 pixel | |

PIXEL_TRANSFORM_OPERATOR_SGI GetIntegerv Z2 CONVOLUTION pixel | |

PIXEL_TRANSFORM_SGI IsEnabled B TRUE pixel/enable | |

New Implementation Dependent State | |

Get Value Get Command Type Minimum Value | |

--------- ----------- ---- ------------- | |

MAX_FFT_WIDTH_SGI GetPixelTransformParameterivSGI 1 x Z+ 256 |