C++ OpenGL (with SOIL addon) - Texture coming out shaded

Question

I'm trying to learn OpenGL but I've not yet got the hang of it, as I encountered a problem at the first hurdle where I try to display a bright red square, but the image comes out as a maroon coloured square. (I apologize but I cannot post pictures due to not having enough reputation :( )

I've been using the SOIL library (http://www.lonesock.net/soil.html) to make the task of loading textures simpler, and I am fairly sure that this is where the problem lies.

I understand the most obvious answer is to not use SOIL, and to learn raw OGL first before I try using extensions, and I do intend to do this. However I would still like this problem solving for peace of mind.

My personal assumption is I have probably enabled some sort of shading somewhere, or there is some quirk of OGL or SOIL that forces the shade of the texture to change, however I am not experienced enough to solve this.

Below is what I believe to be the relevant code.

void displayBackground()
{
    GetTexture("resources/red.png");
    glBegin(GL_QUADS);
        glTexCoord2f(0, 0); glVertex2f(0, 0);
        glTexCoord2f(480, 0); glVertex2f( 480, 0);
        glTexCoord2f(480, 480); glVertex2f( 480,  480);
        glTexCoord2f(0, 480); glVertex2f(0,  480);
    glEnd();
    glDisable(GL_TEXTURE_2D);
}

And below is the SOIL-specific code which as far as I can tell should load a solid red texture into the active OGL texture

GLuint GetTexture(std::string Filename)
{
    GLuint tex_ID;

    tex_ID = SOIL_load_OGL_texture(
                Filename.c_str(),
                SOIL_LOAD_AUTO,
                SOIL_CREATE_NEW_ID,
                SOIL_FLAG_POWER_OF_TWO
                | SOIL_FLAG_MIPMAPS
                | SOIL_FLAG_COMPRESS_TO_DXT
                | SOIL_FLAG_DDS_LOAD_DIRECT
                );

        if( tex_ID > 0 )
        {
            glEnable( GL_TEXTURE_2D );
            glBindTexture( GL_TEXTURE_2D, tex_ID );

            return tex_ID;
        }
        else
            return 0;
}

Thank you in advance for anyone insight into where I have possibly gone wrong.

@Nazar554 I'm assuming this is what you mean by the view port? Sorry, I'm aware this is very basic OGL stuff and I probably sound rather stupid, but you've got to start somewhere right? :P

/** OpenGL Initial Setup**/
    //pixel format descriptor to describe pixel layout of a given surface
    PIXELFORMATDESCRIPTOR pfd;
    std::memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
    pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
    pfd.nVersion = 1;
    pfd.dwFlags = PFD_DRAW_TO_WINDOW |
                PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER_DONTCARE;
    pfd.iPixelType = PFD_TYPE_RGBA;
    pfd.cColorBits = 32;
    pfd.cDepthBits = 16;
    pfd.iLayerType = PFD_MAIN_PLANE;

    HDC hdc = GetDC(hwnd); //gets device context of hwnd. Device context is a set of graphics objects that define how to draw to the given device
    int format = ChoosePixelFormat(hdc, &pfd); //chooses best pixel format for device context given the pfd to be used
    SetPixelFormat(hdc, format, &pfd);
    HGLRC hglrc;
    hglrc = wglCreateContext(hdc); //creates OGL rendering context suitable for drawing on the device specified by hdc
    wglMakeCurrent(hdc, hglrc); //makes hglrc the thread's current context. subsequent OGL calls made on hdc

    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);  // Red, Green, Blue, Alpha. (Additive color) Does not need to be updated every cycle
    glOrtho(0, 900, 600, 1.0, -1.0, 1.0); //sets co-ordinates system

@Nazar554 I've appended what I think is the viewport initialization to the end of my original question. — Sammdahamm, Sep 22 '14 at 14:46

score 0 · Answer 1 · answered Sep 22 '14 at 15:13

0

Put glOrtho before glClearColor. Also you need to select projection matrix before calling glOrtho. Use this:

glMatrixMode(GL_PROJECTION); // select projection matrix
glLoadIdentity(); // clear it
glOrtho(0, w, h, 0, 0, 1); // compute projection matrix, and multiply identity matrix by it
// w, h is your window size if you are doing 2D
glMatrixMode(GL_MODELVIEW); // select model matrix

Also, if you are studying OpenGL better begin with modern versions (3.3+, or 2.1 without old stuff), not 1.2. They have a lot of differences and it will be hard to forget everything you studied before. For beginners freeglut or GLFW is more simple and portable than pure Win32.

answered Sep 22 '14 at 15:13

Nazar554

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`Put glOrtho before glClearColor.` The order of these doesn't matter. – Colonel Thirty Two Sep 22 '14 at 15:15
@ColonelThirtyTwo looks cleaner for me that way. keeps matrix stuff separated – Nazar554 Sep 22 '14 at 15:17
I added the code you provided and it all compiled successfully, but unfortunately the image still comes out brown/maroon instead of bright red :( – Sammdahamm Sep 22 '14 at 15:17
Also thank you for the advice on trying modern OGL, that seems like a much better idea! I wasn't actually aware that I was using out of date OGL :P This problem isn't particularly important, because I intend to start over, learning raw OGL without the dependency on SOIL, but I'd rather solve it just in case I happen across a similar problem in the future – Sammdahamm Sep 22 '14 at 15:19

C++ OpenGL (with SOIL addon) - Texture coming out shaded

1 Answers1