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c++opengl-estextures

OpenGL - Simple 2D Texture Not Being Displayed

I have written a very simple OpenGL program using glfw and glew. It compiles fine and runs, but the simple texture I am passing to the fragment shader is not being displayed.

The only geometry is a single quad.

I am only trying to display a single solid color, the first element of the texture. I know that the fragment shader works at all because I can display a solid color without the texture:

#version 320 es
mediump out vec4 color;
precision mediump float;
precision mediump sampler2D;

in vec2 texCoord;
uniform sampler2D tex;

void main() {
    color = vec4(0.5, 0.75, 0.5, 1.0);
}

Simple fragment shader, solid color works

However, when I use the texture sampler I get nothing, like the sampler is sampling only 0s (changing only main()):

void main() {
    color = vec4(texture(tex, vec2(0, 0)).rgb, 1);
}

enter image description here

I am populating and generating the texture in what I believe is the correct manner (TEX_SIZE is defined as #define TEX_SIZE (32*32)):

//Texture Data
GLfloat texData[TEX_SIZE * 3] = {1.0};

//Create texture
GLuint tex;
glGenTextures(1, &tex);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 32, 32, 0, GL_RGB, GL_FLOAT, texData);
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_WRAP_R, GL_REPEAT);

And here is the entire draw loop:

//Render loop
while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS
    && !glfwWindowShouldClose(window)) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glUseProgram(programID);

    //Texture
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, tex);
    glUniform1i(glGetUniformLocation(programID, "tex"), 0);

    //Draw the quad
    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, 0, gVertices);
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, gIndices);
    glDisableClientState(GL_VERTEX_ARRAY);

    if (glGetError()) {
        puts((char *)glewGetErrorString(glGetError()));
    }

    glfwSwapBuffers(window);
    glfwPollEvents();
}

Why is this happening? I'm totally stuck.

EDIT: Changed the array initialization, as per suggestion:

//Texture Data
GLfloat texData[TEX_SIZE * 3];
for (int i = 0; i < TEX_SIZE * 3; i++) {
    texData[i] = 1.0;
}

There was no change. Output is still all black.

Solution

  • The initial value of GL_TEXTURE_MIN_FILTER is GL_NEAREST_MIPMAP_LINEAR. But you don't generate mipmaps. This causes that the texture is not complete.

    OpenGL ES 3.2 Specification; 8.17 Texture Completeness; page 205

    A texture is said to be complete if all the texture images and texture parameters required to utilize the texture for texture application are consistently defined.

    ... a texture is complete unless any of the following conditions hold true:

    • The minification filter requires a mipmap (is neither NEAREST nor LINEAR), and the texture is not mipmap complete.

    Change the texture minification filter (glTexParameteri) to solve your issue:

    e.g.

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);