创建原始OpenGL纹理数据（C ++）

Question

So basically I'm trying to create my own texture in code. Specifically I'm writing a ray tracer and want to display the result as a texture rendered to a quad on the screen.

But how does one exactly go about creating your own texture and then applying it to the screen quad? I've been at this for days without any particular results. What I get now is a quad onto the screen but the texture is one color for the entire quad. But in my example here I want it to be 1/3 white and 2/3 black and this is how I imagine it to be done.

I want to keep OpenGL as barebone as possible. I'm not planning on expanding it so any answer that contains an "ugly hack" is totally fine for as long as it works. I'm using Glew, GLFW and GLM.

This is how I'm currently doing it:

GLFWwindow* window;

//Create a texture that should be 1 third black and 2 thirds white?
unsigned char texdata[SCREEN_HEIGHT * SCREEN_WIDTH * 3];
for(int i=0; i<SCREEN_HEIGHT * SCREEN_WIDTH * 3; i++)
{
    if(i < SCREEN_HEIGHT * SCREEN_WIDTH)
        texdata[i] = 255;
    else
        texdata[i] = 0;
}
//cam.createTexture(texdata);

initOpenGL(window);

GLuint t = 0;

glEnable(GL_TEXTURE_2D); // Required for glBuildMipmap() to work (!)
glGenTextures( 1, &t );
glBindTexture(GL_TEXTURE_2D, t);
// Set parameters to determine how the texture is resized
glTexParameteri ( GL_TEXTURE_2D , GL_TEXTURE_MIN_FILTER , GL_LINEAR_MIPMAP_LINEAR );
glTexParameteri ( GL_TEXTURE_2D , GL_TEXTURE_MAG_FILTER , GL_LINEAR );
// Set parameters to determine how the texture wraps at edges
glTexParameteri ( GL_TEXTURE_2D , GL_TEXTURE_WRAP_S , GL_REPEAT );
glTexParameteri ( GL_TEXTURE_2D , GL_TEXTURE_WRAP_T , GL_REPEAT );
// Read the texture data from file and upload it to the GPU
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SCREEN_WIDTH, SCREEN_HEIGHT, 0,
             GL_RGB, GL_UNSIGNED_BYTE, texdata);
glGenerateMipmap(GL_TEXTURE_2D);

GLuint programID = LoadShaders("vertex.glsl", "fragment.glsl");
glUseProgram(programID);
// Create and compile our GLSL program from the shaders

Objects screenquad;
screenquad.createBox(1.0, 1.0, 0.0);

do{

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    screenquad.render();
    // Swap buffers
    glfwSwapBuffers(window);
    glfwPollEvents();
} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
       glfwWindowShouldClose(window) == 0 );

GLSL shader code:

#version 450

in vec2 Texcoord;

out vec4 outColor;

uniform sampler2D tex;

void main(){
    outColor = texture(tex, Texcoord);
}

And the vertex shader:

#version 450
layout(location = 0) in vec3 vertexPosition_modelspace;
layout(location = 1) in vec3 Normal;
layout(location = 2) in vec2 texcoord;

out vec2 Texcoord;

void main(){
    Texcoord = texcoord;
    gl_Position.xyz = vertexPosition_modelspace;
    gl_Position.w = 1.0;
}

EDIT: Internals of creating the screenquad: https://raw.githubusercontent.com/ddavidtran/Fishualization/master/OpenGL/Objects.cpp

Answer 1

The tex uniform is not set in the code. It could be done roughly like this:

GLint texUniformLocation = glGetUniformLocation(programID, "tex");
glUniform1i(texUniformLocation, 0);

Here, 0 in glUniform1i is the current active texture image unit , which is GL_TEXTURE0 by default. You can change it via glActiveTexture .

However, as BDL noticed, 0 is actually the default value, so you may skip this part.

Another problem is that your texture coordinates are wrong. As seen in the file you linked , in function Objects::createBox , the vertex data is

const GLfloat vertex_array_data[] = {
    -xsize, -ysize, -zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Vertex 0
    xsize, -ysize, -zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Vertex 1
    -xsize, ysize, -zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,  // Vertex 2
    xsize, ysize, -zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,  // Vertex 3
    -xsize, -ysize, zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Vertex 0
    xsize, -ysize, zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Vertex 1
    -xsize, ysize, zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,  // Vertex 2
    xsize, ysize, zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f  // Vertex 3
};

The last two floats in each row are the texture coordinates. As you can see, all of them are 0. The normals are also strange, but you don't use them anyway.

I have no idea what texture coordinates for a box you would like, but for a quad I'd do something like this:

const GLfloat vertex_array_data[] = {
    -xsize, -ysize, -zsize, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Vertex 0
    xsize, -ysize, -zsize, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, // Vertex 1
    -xsize, ysize, -zsize, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f,  // Vertex 2
    xsize, ysize, -zsize, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f,  // Vertex 3
};