Question

For some reason I can’t detect I can’t set a z index for any triangle. The triangle will display, at the same depth, from 1 to -1 (inclusive), but after that it dissapers. I am not applying any MVP matrix (trying to figure out this first) and I would expect to be able to see my triangle get smaller as I decrease the z value. This is what I have so far:

//My main function
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA|GLUT_ALPHA|GLUT_DOUBLE|GLUT_DEPTH);
glutInitWindowSize(640, 480);
glutCreateWindow("Window");

if (init_resources()) {
    glutDisplayFunc(onDisplay);
    glutIdleFunc(idle);
    glEnable(GL_BLEND);
    glEnable(GL_DEPTH_TEST);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glutKeyboardFunc(keyboard);
    glutMouseFunc(mouse);
    glutMainLoop();
}

//And in my display function
glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT);

And with my vertext shader:

gl_Position = vec4(coord2d, 0.0, 1.0);

glGetIntegerv(GL_DEPTH_BITS, &depth) also returns 24.

edit: full code

Sprite *sprite1;
Sprite *sprite2;

GLuint program;
GLuint cameraAttribute;

int init_resources()
{   

    //Link shaders, create program and attach shaders
    GLint link_ok = GL_FALSE;
    GLuint vs, fs;
    if ((vs = create_shader("vertShader.sh", GL_VERTEX_SHADER))   == 0) return 0;
    if ((fs = create_shader("fragShader.sh", GL_FRAGMENT_SHADER)) == 0) return 0;

    program = glCreateProgram();
    glAttachShader(program, vs);
    glAttachShader(program, fs);


    glLinkProgram(program);
    glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
    if (!link_ok) {
        fprintf(stderr, "glLinkProgram:");
        print_log(program);
        return 0;
    }

    //Create Attributes
    cameraAttribute = glGetUniformLocation(program, "camera");
    if(cameraAttribute == -1){
        cout << "Error!";
    }


    //Init sprites
    sprite1 = new Sprite();
    sprite2 = new Sprite();


    return 1;
}

void onDisplay()
{
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT);
    glUseProgram(program);


    sprite1->render();
    sprite2->render();

    glutSwapBuffers();
}

void idle()
{

    //Create Projection Matrix to change clip space.
    mat4 projectionMatrix = perspective(60.0f, (float)glutGet(GLUT_WINDOW_WIDTH) / (float)glutGet(GLUT_WINDOW_HEIGHT), 0.1f, 100.f);
    glUniformMatrix4fv(cameraAttribute, 1, GL_FALSE, &projectionMatrix[0][0]);

}

void free_resources()
{
    glDeleteProgram(program);
}


int main(int argc, char* argv[]) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA|GLUT_ALPHA|GLUT_DOUBLE|GLUT_DEPTH);
    glutInitWindowSize(640, 480);
    glutCreateWindow("My Second Triangle");
    glEnable(GL_BLEND);
    glEnable(GL_DEPTH_TEST);

    if (init_resources()) {
        glutDisplayFunc(onDisplay);
        glutIdleFunc(idle);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

        //uses glGetError to check for how many errors there are.
        cout << CheckGLErrors() << "\n";

        glutMainLoop();
    }


    free_resources();
    return 0;
}

And my sprite file:

#include "Sprite.h"

Sprite::Sprite(){
    init();
}


void Sprite::init(){

    GLfloat triangle_vertices[] = {
        0.0,  0.8f,
        -0.8f, -0.8f,
        0.8f, -0.8f,
    };

    //Set attributes
    locationAttribute = glGetAttribLocation(program, "coord2d");
    if (locationAttribute == -1) {
        fprintf(stderr, "Could not bind attribute location");
    }

    translationUniform = glGetUniformLocation(program, "translationUniform");
    if(translationUniform == -1){
        fprintf(stderr, "Could not bind attribute transformation");
    }


    //Create buffer
    glGenBuffers(1, &mainBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, mainBuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(triangle_vertices), triangle_vertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);

    glVertexAttribPointer(
                          locationAttribute, // attribute
                          2,                 // number of elements per vertex, here (x,y)
                          GL_FLOAT,          // the type of each element
                          GL_FALSE,          // take our values as-is
                          0,                 // no extra data between each position
                          0                  // offset of first element
    );

    glBindBuffer(GL_ARRAY_BUFFER, 0);
}

void Sprite::render(){
    glBindBuffer(GL_ARRAY_BUFFER, mainBuffer);
    glDrawArrays(GL_TRIANGLES, 0, 3);

}

And Vertex shader: (note, versions are added by the parser)

attribute vec2 coord2d;

uniform mat4 translationUniform;
uniform mat4 camera;


void main(void) {

    gl_Position = camera * vec4(coord2d, -1.1, 1.0);
}

Answer 1

glEnable(GL_BLEND | GL_DEPTH_TEST);

You can’t combine these like this, you have to issue two glEnable commands. This is probably generating an error, or enabling something completely different.

You’re confusing this with glClear, which uses bitwise masks.

Start using glGetError in your code, it would have caught this problem for you.