9.5 Cg
Cg is a high-level programming language developped by Nvidia that allows developpers to move away from writing shader code in assembly language. If you have used the FragmentProgram effect, you will realize that making simple programs run on the GPU is no easy task. Cg allows you to write C-like code that is then converted to assembly code by the Cg compiler to be executed on your graphics card. Please be aware that you need to have a programming background to use this effect. More information on Cg can be found here.
9.5.1 Parameters
The most important parameter of the Cg effect is Program using which you give the entire shader in string form to the effect, or pass a path to a file containing the shader program text. Obviously, you’ll want to control some of the parameters of your shader. For that purpose, the Cg effect exposes all the parameters to your shader’s main function as its own parameters automatically. See example below.
| Parameters |
| Default |
| Range |
| Description |
| Program |
| "" |
| n/a |
| The Cg program string or the full path of the text file that contains the Cg program. You *must* set this parameter. |
|
|
|
| ||||
| GlobalMode |
| 1 |
| [0,1] |
| See GlobalMode |
9.5.2 Simple usage
The muvee style below gradually increases the saturation of the input picture.
; muSE v2 ; ; My unbelievably awesome style. ; It manipulates the saturation of the user media. (style-parameters) (segment-durations 8.0)
struct fragment |
{ |
float4 position : POSITION; |
float4 color0 : COLOR0; |
float2 texcoord0 : TEXCOORD0; |
}; |
|
struct pixel |
{ |
float4 color : COLOR; |
}; |
|
pixel main( fragment IN, |
const uniform sampler2D inputTexture, |
const uniform float1 progress) |
{ |
pixel OUT; |
|
float4 texelColor = tex2D( inputTexture, IN.texcoord0 ); |
|
//Let us convert RGB to YUV |
float4 weightY = { 0.29900, 0.58700, 0.11400, 1.0 }; |
float4 weightU = { -0.14713, -0.28886, 0.43600, 1.0 }; |
float4 weightV = { 0.61500, -0.51499, -0.10001, 1.0 }; |
|
float4 Y = weightY * texelColor; |
float4 U = weightU * texelColor; |
float4 V = weightV * texelColor; |
|
float4 YUV; |
YUV.r = Y.r + Y.g + Y.b; |
YUV.g = U.r + U.g + U.b; |
YUV.b = V.r + V.g + V.b; |
|
// |
//Here we manipulate the YUV values |
// |
//YUV.r *= progress; |
YUV.g *= progress * 2.0; |
YUV.b *= progress * 2.0; |
|
//Let's convert YUV back to RGB |
float4 weightR = {1.0, 0.00000, 1.13983, 1.0}; |
float4 weightG = {1.0, -0.39465, -0.58060, 1.0}; |
float4 weightB = {1.0, 2.03211, 0.00000, 1.0}; |
|
float4 R = weightR * YUV; |
float4 G = weightG * YUV; |
float4 B = weightB * YUV; |
|
OUT.color.a = texelColor.a * IN.color0.a; |
OUT.color.r = R.r + R.g + R.b; |
OUT.color.g = G.r + G.g + G.b; |
OUT.color.b = B.r + B.g + B.b; |
|
return OUT; |
} |
(define muvee-global-effect (effect-stack (effect "Perspective" (A)) (effect "CropMedia" (A)))) (define muvee-segment-effect (effect "Cg" (A) (param "Program" program-string) (param "progress" 0.0 (linear 1.0 1.0))))
There is one important thing to note about the above Cg program - the "progress" parameter’s name is the name of the third parameter to the main function of the shader. If you change the name progress to, say, saturation, then you’ll have to write (param "saturation" ...) instead.
pixel main( fragment IN, |
const uniform sampler2D inputTexture, |
const uniform float1 progress) |
We recommend that you use Cg instead of the FragmentProgram effect because it is much easier to learn, write and debug, you make fewer errors and it lets you use advanced features of newer graphics cards when available. Do read NVidia’s CG documentation. Have fun!