Question

I’m currently trying to make a very simple snake game and have some problem creating the snake square. Right now I am creating the squares by creating 2 triangles. I have created the grid where the snake should be moving like this:

The color of the squares were actually yellow in the beginning. Then I tried to create the snake with the color red. But all my squares turned red.

I create the snake like this:

void drawSnake()
{
    mat4 modelView;

    modelView = Translate(1,0,0);
    glUniformMatrix4fv(modelViewUniform, 1, GL_TRUE, modelView);
    GLuint indices2[3] = {0,1,2}; //, 0, 5, 1, 0};

    glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, indices2);

    modelView = Translate(1, 0, 0);
    glUniformMatrix4fv(modelViewUniform, 1, GL_TRUE, modelView);
    GLuint indices6[3] = {4,3,2}; //, 0, 5, 1, 0};
    glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, indices6);
    //vec2 blockCoordinate = vec2(-t + 1, t - 1);
    //blockCol[i] = blockCoordinate;
}

The colors defined here:

void loadGeometry() {
    vec3 color(1.0f, 1.0f, 0.0f);
    Vertex rectangleData[rectangleSize] = {
        { vec2( -1.0, -1.0 ), color },
        { vec2( 1.0, -1.0 ), color },
        { vec2( 1.0,  1.0 ), color },
        { vec2( -1.0,  1.0 ), color },
        { vec2(-1.0, -1.0 ), color }
    };
    shapeVertexArrayBuffer = loadBufferData(rectangleData, rectangleSize);

    vec3 color1(1.0f, 0.0f, 0.0f);
    Vertex rectangleData1[rectangleSize] = {
        { vec2( -1.0, -1.0 ), color1 },
        { vec2( 1.0, -1.0 ), color1 },
        { vec2( 1.0,  1.0 ), color1 },
        { vec2( -1.0,  1.0 ), color1 },
        { vec2(-1.0, -1.0 ), color1 }
    };
    shapeSnakeArrayBuffer = loadBufferData(rectangleData1, rectangleSize);
}

So the question is why all my squares turned red when I obviously load the buffer data with another color?

I draw them like this in the display():

void display() {    
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(shaderProgram);

    mat4 projection = Ortho2D(-15.0f, 15.0f, -15.0f, 15.0f);
    glUniformMatrix4fv(projectionUniform, 1, GL_TRUE, projection);

    glBindVertexArray(shapeVertexArrayBuffer);
    glBindVertexArray(shapeSnakeArrayBuffer);

    drawBlock();
    drawSnake();
    glutSwapBuffers();
}

Answer 1

glBindVertexArray(shapeVertexArrayBuffer);
glBindVertexArray(shapeSnakeArrayBuffer);

drawBlock();
drawSnake();

You seem to have some ordering problems here. Presumably the shapeVertexArrayBuffer (note: there’s no such thing as a “vertex array buffer”. Those are supposed to be vertex array objects; if loadBufferData doesn’t return a VAO, then you have more problems) is meant for drawing blocks, and the shapeSnakeArrayBuffer is meant for drawing the snake.

You can only have one VAO active at a time. glBindVertexArray sets the given vertex array object to be what is used for all rendering commands after it. Since the last one you used was shapeSnakeArrayBuffer, that will be the VAO used for all rendering commands in drawBlock just as well as for drawSnake.