twist effect

[huaner]

hi:
i write a effect of shader that a quad has two texture and the second texture inside the first texure.the shader as fellow:

 
vertex:
varying vec2 tex1;
void main()
{
	gl_TexCoord[0] = gl_MultiTexCoord0;
	gl_TexCoord[1] = gl_MultiTexCoord0;
	tex1 = gl_MultiTexCoord0;
	gl_Position = ftransform();
} 
fragment:
uniform sampler2D TextureUnit0;
uniform sampler2D TextureUnit1;
varying vec2 tex1;
void main()
{	
	vec4 value1 = texture2D(TextureUnit0, gl_TexCoord[0]);
	vec4 value2 = texture2D(TextureUnit1, gl_TexCoord[1]);

	if(tex1.x >= 0.2 && tex1.y >= 0.2 &&
		tex1.x <= 0.8 && tex1.y <= 0.8)
		gl_FragColor = value2;
	else
		gl_FragColor = value1;
}
 

the problem is there is a black quad below the effect quad, and turn back the background picture. May the texture coordnate that i deal with is wrong?

[predaeus]

again I think you want

gl_TexCoord[1] = gl_MultiTexCoord1;

[huaner]

Hi:
predaeus. if i rectify it by

gl_TexCoord[1] = gl_MultiTexCoord1;
  

the result is aslo wrong. and i have side if i complie ogl procedure with this shader, the result is right.

[kewuwsi]

looks the shaders are OK, seems the two textures are sharing same coordinates(gl_TexCoord[0] == gl_TexCoord[1]).
So, check the OGL application to make sure the two textures are aligned well.
also, I think you don’t have to use the variable tex1,since gl_TexCoord[0] == tex1

[kewuwsi]

suggestion: use “subimage” to make this more simple.

[system]

As far as I know, it should not even compile

This
vec4 value1 = texture2D(TextureUnit0, gl_TexCoord[0]);

should be

vec4 value1 = texture2D(TextureUnit0, gl_TexCoord[0].xy);

Here is a optimized version of your shader

vertex:

void main()
{
	gl_TexCoord[0].xy = gl_MultiTexCoord0.xy;

	gl_Position = ftransform();
}
 
fragment:
uniform sampler2D TextureUnit0;
uniform sampler2D TextureUnit1;

void main()
{	
	vec4 value1 = texture2D(TextureUnit0, gl_TexCoord[0].xy);
	vec4 value2 = texture2D(TextureUnit1, gl_TexCoord[0].xy);

	if(gl_TexCoord[0].x >= 0.2 && gl_TexCoord[0].y >= 0.2 &&
		gl_TexCoord[0].x <= 0.8 && gl_TexCoord[0].y <= 0.8)
		gl_FragColor = value2;
	else
		gl_FragColor = value1;
}

[kewuwsi]

yes! thanks for the correction.