Hello to everybody,
I try to implement a soft shadow with PCF so, I’m writing a glsl test to visualize the z value:
"void main(void)
"
"{
"
" gl_Position = ftransform();
"
" gl_TexCoord[0] = gl_MultiTexCoord0;
"
" vec4 ecPosition = gl_ModelViewMatrix * gl_Vertex;
"
" vectLighttoVertex = lightPos - gl_Position;
"
" projCoord .s = dot(ecPosition, gl_EyePlaneS[3]);
"//multiply light view matrix
" projCoord .t = dot(ecPosition, gl_EyePlaneT[3]);
"
" projCoord .p = dot(ecPosition, gl_EyePlaneR[3]);
"
" projCoord .q = dot(ecPosition, gl_EyePlaneQ[3]);
"
"}
";
// fragment shader program for bump mapping in surface local coordinates
static std::string _fp_program =
"uniform sampler2D sampler2d;
"
"uniform sampler2D shadowMap;
"
"const float c = 1.0f/128.0f;
"
"varying vec4 projCoord;
"
"varying vec4 vertexNormal;
"
"varying vec4 vectLighttoVertex;
"
"void main (void)
"
"{
"
" vec3 finalColor;
"
" float actShadow;
"
" vec3 color = vec3(texture2D(sampler2d, vec2 (gl_TexCoord[0])));
"
" vec3 projectiveBiased = (projCoord.xyz / projCoord.w);
"
//get the 4 z value from the shadow map
" vec4 shadowValue0 = texture2D(shadowMap, projectiveBiased.xy );
"
" vec4 shadowValue1 = texture2D(shadowMap, projectiveBiased.xy + vec2( c,0 ) );
"
" vec4 shadowValue2 = texture2D(shadowMap, projectiveBiased.xy + vec2( c,c ) );
"
" vec4 shadowValue3 = texture2D(shadowMap, projectiveBiased.xy + vec2( 0,c ) );
"
//perform the shadow map test if pass
" actShadow = 0.0f;
"
" if ( shadowValue0.z > projectiveBiased.z )
"
" actShadow += 1.0f;
"
" if ( shadowValue1.z > projectiveBiased.z )
"
" actShadow += 1.0f;
"
" if ( shadowValue2.z > projectiveBiased.z )
"
" actShadow += 1.0f;
"
" if ( shadowValue3.z > projectiveBiased.z )
"
" actShadow += 1.0f;
"
//perform the PCF
" actShadow /= 1.0f;
"
//assign the final color
" gl_FragColor = vec4( projectiveBiased.z-shadowValue0.z,projectiveBiased.z-shadowValue0.z,projectiveBiased.z-shadowValue0.z,1);
"
"}
";
this is my shader,it show on sceen the z difference between the actual z value and the z value stored in shadow map. It works fine: it show me white color( or a grey) where there is shadow and black where not.
Now I want to see the difference between shadowvalue1/2/3 ( the value taken from 3 near texel) and actual z value
so i switch this line of code:
" gl_FragColor = vec4( projectiveBiased.z-shadowValue0.z,projectiveBiased.z-shadowValue0.z,projectiveBiased.z-shadowValue0.z,1);
"
"}
";
with:
" gl_FragColor = vec4( projectiveBiased.z-shadowValue1.z,projectiveBiased.z-shadowValue1.z,projectiveBiased.z-shadowValue1.z,1);
"
"}
";
but now there are many problems:
It show me everything black!!!That is shadowValue1.z is always greater than actual z (projectiveBiased.z). It seems that I don’t take the correct z value from the shadow map…but…the dimension is 128x128 and this line of code seems correct:
" vec4 shadowValue1 = texture2D(shadowMap, projectiveBiased.xy + vec2( c,0 ) );
"
where c= 1.0f/128.0f
where I make mistake??? 
Thanks Davide