Hi, I m a newbie to both GLSL and this forum

Anyway, I’m trying to implement screen space effect, and ATI’s RenderMonkey help me to concentrate on GLSL itself. My question is this, when I tried to implement screen space effect with GLSL, I’ve got into strange problems.

In vertex shader, I used the quad vertices(which has coordinate range from -1 to 1) directly without applying any matrix transformation. That is,

```
uniform sampler2D Texture0;
varying vec2 TexCoord;
void main(void)
{
gl_Position.xy = sign(gl_Vertex.xy);
gl_Position.w=1.0;
gl_Position.z=0.0;
TexCoord.x=(gl_Vertex.x+1.0) * 0.5;
TexCoord.y=(gl_Vertex.y+1.0) * 0.5;
}
```

For a screen quad mesh, each component of gl_Vertex always range from -1 to 1, so I can directly assign gl_Vertex to gl_Position. TexCoord is used later in the fragment program.

Fragment program is even simpler. That is,

```
uniform sampler2D Texture0;
varying vec2 TexCoord;
void main(void)
{
vec4 c0= texture2D(Texture0, TexCoord);
gl_FragColor = c0;
}
```

I thouth these two shader would display the texture named “Texture0” directly on screen, but it only display a full black rectangle without any colored pixel. That makes me crazy, because the program itself is so simple that nothing can be wrong. To find out the problem, I tried the following vertex shader ,

```
uniform sampler2D Texture0;
varying vec2 TexCoord;
void main(void)
{
// gl_Position.xy = sign(gl_Vertex.xy);
// gl_Position.w=1.0;
// gl_Position.z=0.0;
TexCoord.x=(gl_Vertex.x+1.0) * 0.5;
TexCoord.y=(gl_Vertex.y+1.0) * 0.5;
gl_Position=gl_ModelViewProjectionMatrix * gl_Vertex;
}
```

With the same fragment shader, it displays OK. But what I intended is not this vertex shader(not a fully screen aligned quad).

Whew, thanks for reading boring wrong thread. Is there anything wrong with the first two shaders? Any reply or suggestins would be appreciated.