OpenGL ES 2.0纹理无法显示

Question

So I am currently learning OpenGL ES 2.0 with iOS and working on a maze game. The maze is randomly generated (so not a loaded model) and my struggle is texturing the walls and floor of the maze. My approach is to just treat the maze as a series of cubes, and I have code that draws the individual faces of a cube separately (so I can create a path by simply leaving some faces out).

Using capture GPU frame, I have confirmed that the texture is indeed loading in correctly, the data in the frame buffers is correct and that I'm not getting any errors. I can see my other lighting effects (so the face isn't completely black), but no texture appears.

Here is how I've defined my cube faces

 GLfloat rightCubeVertexData[] =
{
    0.5f, -0.5f, -0.5f,
    0.5f, -0.5f, 0.5f,
    0.5f, 0.5f, -0.5f,
    0.5f, 0.5f, -0.5f,
    0.5f, -0.5f, 0.5f,
    0.5f, 0.5f, 0.5f,
};

GLfloat rightCubeNormalData[] =
{
    -1.0f, 0.0f, 0.0f,
    -1.0f, 0.0f, 0.0f,
    -1.0f, 0.0f, 0.0f,
    -1.0f, 0.0f, 0.0f,
    -1.0f, 0.0f, 0.0f,
    -1.0f, 0.0f, 0.0f,
};

GLfloat rightCubeTexCoords[] =
{
    0.0, 0.0,
    1.0, 0.0,
    0.0, 1.0,
    0.0, 1.0,
    1.0, 0.0,
    1.0, 1.0,
};

The other faces are defined essentially the same way (except they are in one array each, splitting up the position, normals, and tex coords was just something I tried; I'm just trying to get one face to texture and then I'll expand to the rest).

Here is how I load the data into the buffer

glGenVertexArraysOES(1, &_rightVertexArray);
glBindVertexArrayOES(_rightVertexArray);

glGenBuffers(3, _rightVertexBuffer);

glBindBuffer(GL_ARRAY_BUFFER, _rightVertexBuffer[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(rightCubeVertexData), rightCubeVertexData, GL_STATIC_DRAW);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 12, BUFFER_OFFSET(0));

glBindBuffer(GL_ARRAY_BUFFER, _rightVertexBuffer[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(rightCubeNormalData), rightCubeNormalData, GL_STATIC_DRAW);
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 12, BUFFER_OFFSET(0));

glBindBuffer(GL_ARRAY_BUFFER, _rightVertexBuffer[2]);
glBufferData(GL_ARRAY_BUFFER, sizeof(rightCubeTexCoords), rightCubeTexCoords, GL_STATIC_DRAW);
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, 12, BUFFER_OFFSET(0));

Again, using three buffers was an experiment, the rest are defined in one buffer with an offset.

Here is how I load textures

crateTexture = [self setupTexture:@"crate.jpg"];
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, crateTexture);
glUniform1i(uniforms[UNIFORM_TEXTURE], 0);

// Load in and set up texture image (adapted from Ray Wenderlich)
- (GLuint)setupTexture:(NSString *)fileName
{
    CGImageRef spriteImage = [UIImage imageNamed:fileName].CGImage;
    if (!spriteImage) {
        NSLog(@"Failed to load image %@", fileName);
        exit(1);
    }

    size_t width = CGImageGetWidth(spriteImage);
    size_t height = CGImageGetHeight(spriteImage);

    GLubyte *spriteData = (GLubyte *) calloc(width*height*4, sizeof(GLubyte));

    CGContextRef spriteContext = CGBitmapContextCreate(spriteData, width, height, 8, width*4, CGImageGetColorSpace(spriteImage), kCGImageAlphaPremultipliedLast);

    CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), spriteImage);

    CGContextRelease(spriteContext);

    GLuint texName;
    glGenTextures(1, &texName);
    glBindTexture(GL_TEXTURE_2D, texName);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, spriteData);

    free(spriteData);
    return texName;
}

Then, at the appropriate time, I simply call glDrawArrays to draw the face. I am completely stumped on this, and it is probably a very silly error, but any help anybody could provide would be much appreciated.

PS Here is my fragment shader

varying vec3 eyeNormal;
varying vec4 eyePos;
varying vec2 texCoordOut;

uniform sampler2D texture;

uniform vec3 flashlightPosition;
uniform vec3 diffuseLightPosition;
uniform vec4 diffuseComponent;
uniform float shininess;
uniform vec4 specularComponent;
uniform vec4 ambientComponent;

void main()
{
    vec4 ambient = ambientComponent;

    vec3 N = normalize(eyeNormal);
    float nDotVP = max(0.0, dot(N, normalize(diffuseLightPosition)));
    vec4 diffuse = diffuseComponent * nDotVP;

    vec3 E = normalize(-eyePos.xyz);
    vec3 L = normalize(flashlightPosition - eyePos.xyz);
    vec3 H = normalize(L+E);
    float Ks = pow(max(dot(N, H), 0.0), shininess);
    vec4 specular = Ks*specularComponent;
    if( dot(L, N) < 0.0 ) {
        specular = vec4(0.0, 0.0, 0.0, 1.0);
    }

    gl_FragColor = (ambient + diffuse + specular) * texture2D(texture, texCoordOut);
    //gl_FragColor = ambient + diffuse + specular;
    gl_FragColor.a = 1.0;
}

And yes, all the uniform names are correct and correspond to something in the main code.

EDIT: Here is the vertex shader

precision mediump float;

attribute vec4 position;
attribute vec3 normal;
attribute vec2 texCoordIn;

varying vec3 eyeNormal;
varying vec4 eyePos;
varying vec2 texCoordOut;

uniform mat4 modelViewProjectionMatrix;
uniform mat4 modelViewMatrix;
uniform mat3 normalMatrix;

void main()
{
    eyeNormal = (normalMatrix * normal);
    eyePos = modelViewMatrix * position;
    texCoordOut = texCoordIn;
    gl_Position = modelViewProjectionMatrix * position;
}

Answer 1

Turns out I had forgotten to bind the attribute location when compiling the shader. Needed to add the line

glBindAttribLocation(_program, GLKVertexAttribTexCoord0, "texCoordIn");

to the load shaders method.

Answer 2

To sum up the procedure done from the comments...

There is much that can go wrong when dealing with textures and it is good to know how to pinpoint where the issue is.

What to be careful wit the texture itself:

• Check if you did set the parameters such as

   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); 

• Check setting the uniform as glUniform1i(uniformName, 0) where the last parameter corresponds to the active texture and not the texture ID.
• Other include checking if the uniform name is correct, texture is bound.. And if possible check the debugger if the texture is properly loaded.

Next to that there are chances your texture coordinates are messed up and this seems to be a very common issue. To debug that it is best that you replace the color gotten from the texture in your fragment shader with the texture coordinate itself. Eg replace texture2D(texture, texCoordOut) with vec4(texCoordOut.x, texCoordOut.y, .0, 1.0) . Since the texture coordinates should be in range [0,1] you should see nice gradients between red and green color in your scene. If you do not see them then your texture coordinates are messed up: If all is black your coordinates are all zero, if most is yellow then your coordinates are most likely too large.

In your case the texture coordinates were all black which means you were always getting the first pixel from the texture thus a constant color in your scene. What to check at this point is:

• Are the coordinates you push to the GPU correct
• Is the pointer set correctly as glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, 12, BUFFER_OFFSET(0)) (check all the parameters)
• Is the attribute enabled glEnableVertexAttribArray(GLKVertexAttribTexCoord0)
• Is the attribute bound to the shader being compiled.

In your case you have forgotten to bind the texture coordinate attribute which is quite natural to miss.

From the information you have given us it is impossible to find this mistake but you should note the procedure I have given you to pinpoint the issue as to where it actually lies. It might be handy in future as well.