Multiple textures in GLSL - only one works - opengl

Question

My problem is getting more than one texture accessible in a GLSL shader.
Here's what I'm doing:
Shader:
uniform sampler2D sampler0;
uniform sampler2D sampler1;
uniform float blend;
void main( void )
{
vec2 coords = gl_TexCoord[0];
vec4 col = texture2D(sampler0, coords);
vec4 col2 = texture2D(sampler1, coords);
if (blend > 0.5){
gl_FragColor = col;
} else {
gl_FragColor = col2;
}
};
So, I simply choose between the two color values based on a uniform variable. Simple enough (this is a test), but instead of the expected behavior, I get all black when blend <= 0.5.
OpenGL code:
m_sampler0location = m_shader.FindUniform("sampler0");
m_sampler1location = m_shader.FindUniform("sampler1");
m_blendlocation = m_shader.FindUniform("blend");
glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_2D);
m_extensions.glUniform1iARB(m_sampler0location, 0);
glBindTexture(GL_TEXTURE_2D, Texture0.Handle);
glActiveTexture(GL_TEXTURE1);
glEnable(GL_TEXTURE_2D);
m_extensions.glUniform1iARB(m_sampler1location, 1);
glBindTexture(GL_TEXTURE_2D, Texture1.Handle);
glBegin(GL_QUADS);
//lower left
glTexCoord2f(0, 0);
glVertex2f(-1.0, -1.0);
//upper left
glTexCoord2f(0, maxCoords0.t);
glVertex2f(-1.0, 1.0);
//upper right
glTexCoord2f(maxCoords0.s, maxCoords0.t);
glVertex2f(1.0, 1.0);
//lower right
glTexCoord2f(maxCoords0.s, 0);
glVertex2f(1.0, -1.0);
glEnd()
The shader is compiled and bound before all this. All the sanity checks in that process indicate that it goes ok.
As I said, the value of col in the shader program reflects fragments from a texture; the value of col2 is black. The texture that is displayed is the last active texture - if I change the last glBindTexture to bind Texture0.Handle, the texture changes. Fixed according to Bahbar's reply.
As it is, the scene renders all black, even if I add something like gl_FragColor.r = blend; as the last line of the shader. But, if I comment out the call glActiveTexture(GL_TEXTURE1);, the shader works again, and the same texture appears in both sampler0 and sampler1.
What's going on? The line in question, glActiveTexture(GL_TEXTURE1);, seems to work just fine, as evidenced by a subsequent glGetIntegerv(GL_ACTIVE_TEXTURE, &anint). Why does it break everything so horribly? I've already tried upgrading my display drivers.

Answer 1

Here's a basic GLUT example (written on OS X, adapt as needed) that generates two checkerboard textures, loads a shader with two samplers and combines them by tinting each (one red, one blue) and blending. See if this works for you:
#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#define kTextureDim 64
GLuint t1;
GLuint t2;
/* adapted from the red book */
GLuint makeCheckTex() {
GLubyte image[kTextureDim][kTextureDim][4]; // RGBA storage
for (int i = 0; i < kTextureDim; i++) {
for (int j = 0; j < kTextureDim; j++) {
int c = ((((i & 0x8) == 0) ^ ((j & 0x8)) == 0))*255;
image[i][j][0] = (GLubyte)c;
image[i][j][1] = (GLubyte)c;
image[i][j][2] = (GLubyte)c;
image[i][j][3] = (GLubyte)255;
}
}
GLuint texName;
glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, kTextureDim, kTextureDim, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
return texName;
}
void loadShader() {
#define STRINGIFY(A) #A
const GLchar* source = STRINGIFY(
uniform sampler2D tex1;
uniform sampler2D tex2;
void main() {
vec4 s1 = texture2D(tex1, gl_TexCoord[0].st);
vec4 s2 = texture2D(tex2, gl_TexCoord[0].st + vec2(0.0625, 0.0625));
gl_FragColor = mix(vec4(1, s1.g, s1.b, 0.5), vec4(s2.r, s2.g, 1, 0.5), 0.5);
}
);
GLuint program = glCreateProgram();
GLuint shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(shader, 1, &source, NULL);
glCompileShader(shader);
GLint logLength;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
if (logLength > 0) {
GLchar* log = (GLchar*)malloc(logLength);
glGetShaderInfoLog(shader, logLength, &logLength, log);
printf("Shader compile log:\n%s\n", log);
free(log);
}
glAttachShader(program, shader);
glLinkProgram(program);
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLength);
if (logLength > 0) {
GLchar* log = (GLchar*)malloc(logLength);
glGetProgramInfoLog(program, logLength, &logLength, log);
printf("Program link log:\n%s\n", log);
free(log);
}
GLuint t1Location = glGetUniformLocation(program, "tex1");
GLuint t2Location = glGetUniformLocation(program, "tex2");
glUniform1i(t1Location, 0);
glUniform1i(t2Location, 1);
glUseProgram(program);
}
void init()
{
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_FLAT);
t1 = makeCheckTex();
t2 = makeCheckTex();
loadShader();
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, t1);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, t2);
glBegin(GL_QUADS);
//lower left
glTexCoord2f(0, 0);
glVertex2f(-1.0, -1.0);
//upper left
glTexCoord2f(0, 1.0);
glVertex2f(-1.0, 1.0);
//upper right
glTexCoord2f(1.0, 1.0);
glVertex2f(1.0, 1.0);
//lower right
glTexCoord2f(1.0, 0);
glVertex2f(1.0, -1.0);
glEnd();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-2, 2, -2, 2, -2, 2);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_DEPTH | GLUT_RGBA);
glutInitWindowSize(512, 512);
glutInitWindowPosition(0, 0);
glutCreateWindow("GLSL Texture Blending");
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutIdleFunc(display);
init();
glutMainLoop();
return 0;
}
Hopefully the result will look something like this (you can comment out the glUseProgram call to see the first texture drawn without the shader):

Answer 2

Just to help other people who might be interested in using multiple textures and will feel hopeless after days searching for an answer. I found that you need to call
glUseProgram(program);
GLuint t1Location = glGetUniformLocation(program, "tex1");
GLuint t2Location = glGetUniformLocation(program, "tex2");
glUniform1i(t1Location, 0);
glUniform1i(t2Location, 1);
In that order for it to work (glUseProgram is the last instruction for 99% of the sample code I've found online). Now it may be only the case for me and not affect anyone else on Earth, but just in case I thought I'd share.

Answer 3

Quite late reply, but for anybody encountering this - I encountered same problem and after short fiddling, I realized that calling glActiveTexture(GL_TEXTURE0) fixes the issue.
It seems something down the line gets confused if active texture unit is not 'reset' to zero.
This could be system-dependent behavior; I'm running 64bit Archlinux with Mesa 8.0.4.

Answer 4

When compiling your shader to test, I found two errors:
coords should be assigned the st portion of the 4-component gl_TexCoord, e.g.
vec2 coords = gl_TexCoord[0].st;
The shader should not end with a semicolon.
Are you checking anywhere in your main program that shader compiles correctly? You may want to look at GL_COMPILE_STATUS via glGetShader and glGetShaderInfoLog.

Answer 5

It sounds like your glActiveTexture call does not work. Are you sure you set up the function pointer correctly ?
Verify by calling glGetIntegerv(GL_ACTIVE_TEXTURE, &anint) after having called your glActiveTexture(GL_TEXTURE1).
Also glEnable(GL_TEXTURE_2D) are not useful. The shader itself specifies what texture units to use, and which target of each unit to "enable".
Edit to add:
Well, your new situation is peculiar. The fact that you can't even show red is weird, in particular (well, did you set alpha to 1 just to make sure ?).
That said, you should restore GL_TEXTURE0 as the glActiveTexture after you're done setting the texture unit 1 (i.e. after the glBindTexture call).