Rewrite GLSL to CG.

Hello, my name is Denis. I found some shader in GLSL for Unity and i want to rewrite it in CG.

This is code:

Code (csharp):

1. Shader "Custom/ShaderMB"
2. {    
3.     Properties
4.     {
5.         _MainTex ("Base (RGB)", 2D) = "white" {}
6.     }
7.     SubShader
8.     {
9.         Tags { "Queue" = "Geometry" }
10.         Pass
11.             {            
12.                 GLSLPROGRAM                          
13.                 #ifdef VERTEX  
14.                
15.                 varying vec2 the_uv;
16.                
17.                 void main()
18.                 {          
19.                     gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
20.                     the_uv = gl_MultiTexCoord0.st;
21.                 }
22.                 #endif  
23.  
24.                 #ifdef FRAGMENT
25.                 #include "UnityCG.glslinc"
26.                 uniform sampler2D _MainTex;
27.                 varying vec2 the_uv;
28.                
29.                 vec3 deform( in vec2 p, float scale )
30.                 {
31.                     vec2 uv;
32.                    
33.                     float mtime = scale+_Time.y;
34.                     float a = atan(p.y,p.x);
35.                     float r = sqrt(dot(p,p));
36.                     float s = r * (1.0+0.5*cos(mtime*1.7));
37.                
38.                     uv.x = .1*mtime +.05*p.y+.05*cos(-mtime+a*3.0)/s;
39.                     uv.y = .1*mtime +.05*p.x+.05*sin(-mtime+a*3.0)/s;
40.                
41.                     float w = 0.8-0.2*cos(mtime+3.0*a);
42.                
43.                     vec3 res = texture2D(_MainTex,uv).xyz*w;
44.                     return  res*res;
45.                
46.                 }
47.                
48.                 void main(void)
49.                 {
50.                     vec2 p = -1.0 + 2.0 * gl_FragCoord.xy / _ScreenParams.xy;
51.                     vec3 total = vec3(0.0);
52.                     float w = 0.0;
53.                     for( int i=0; i<20; i++ )
54.                     {
55.                         vec3 res = deform(p,w);
56.                         total += res;
57.                         w += 0.02;
58.                     }
59.                     total /= 20.0;
60.                
61.                     gl_FragColor = vec4( 3.0*total,1.0);
62.                 }
63.            
64.                 #endif                          
65.                 ENDGLSL        
66.             }
67.      }
68.     FallBack "Diffuse"
69. }

I'm stuck at

Code (csharp):

1. vec2 p = -1.0 + 2.0 * gl_FragCoord.xy / _ScreenParams.xy;

. Could somebody explain me, how it will be in CG?

Please, help!

 

I think I never found out how to do this in Cg vertex and fragment shaders. (Supposedly, it is a particular semantic, but I couldn't get that to work.)
In a Surface Shader it is the screenPos member of the Surface Shader input structure: http://docs.unity3d.com/Documentation/Components/SL-SurfaceShaders.html

 

gl_FragCoord = VPOS semantic in cg.

EDIT: VPOS is for shader model 3.0. If you need it in 2.0, you must calculate it manually and pass it to your fragment shader via a TEXCOORD.

 

And next question... How to setup VPOS? gl_FragCoord is read-only and already contains the window relative coordinate.

 

For basic syntax of Cg shaders, see http://en.wikibooks.org/wiki/Cg_Programming/Unity

 

This link explains how to generate VPOS if semantic itself is not supported.

EDIT: Check the gamedev link provided at the bottom too.