Changing the texture displayed in fragment shader - opengl

Question

I am trying to pass 2 textures to a shader and I am a little confused about the working here
This is the opengl code
GLuint textures;
GLuint textures1;</code>
glGenTextures(1,&textures);
glGenTextures(1,&textures1);
glBindTexture(GL_TEXTURE_2D,textures);
glTexImage2D(GL_TEXTURE_2D,0,GL_RGB,256,256,0,GL_RGB,GL_UNSIGNED_BYTE,texImg);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
glBindTexture(GL_TEXTURE_2D,textures1);
glTexImage2D(GL_TEXTURE_2D,0,GL_RGB,256,256,0,GL_RGB,GL_UNSIGNED_BYTE,texImg1);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
glBindTexture(GL_TEXTURE_2D,textures1);
GLuint location1=glGetUniformLocation(programObjectFloor,"Tex1");
GLuint location2=glGetUniformLocation(programObjectFloor,"Tex2");
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D,textures1);
glUniform1i(location2, 1);
glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,textures);
glUniform1i(location1, 0);
The Vertex Shader is
attribute vec4 position;
attribute vec4 texture;
uniform mat4 MVP;
varying vec4 ptexture;
void main()
{
ptexture = texture;
gl_Position = MVP * position;
}
The Fragment Shader is
varying vec4 ptexture;
uniform sampler2D Tex1;
uniform sampler2D Tex2;
uniform bool swit;
void main()
{
gl_FragColor = texture2D(Tex1,ptexture.st);
}
When I change the line
gl_FragColor = texture2D(Tex2,ptexture.st);
Still only the first texture is shown, but when I comment out the below lines, the second texture is shown, can you please explain why this is happening?
// glActiveTexture(GL_TEXTURE0);
// glEnable(GL_TEXTURE_2D);
// glBindTexture(GL_TEXTURE_2D,textures);
// glUniform1i(location1, 0);

Answer 1

You must call glUseProgram before querying for the uniform locations and assinging values to them. Most likely you're switching the program later, leaving whatever you set those uniforms to in a undefined state.
Also when using shaders, there's no need for glEnable(GL_TEXTURE_2D);, if the texture is used or not is determined by the shader's code.
Not related to your problem, just pointing out, you have a redundant call to glBindTexture just before you query the uniform locations.