Sign in to follow this  

OpenGL Help with the basics...

This topic is 1841 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Why am I not seeing a red triangle on my blue screen?

#pragma comment(linker, "/subsystem:windows")
#include <windows.h>
#pragma comment (lib, "openGL32")
#include <gl/gl.h>
#include <gl/glu.h>
bool fullScreen = true;
void Render()
    glMatrixMode( GL_MODELVIEW );
glColor4f(1.0f, 0.0f, 0.0f, 0.0f);

float zPos = -10.0f;
glVertex3f(100.0f, 100.0f, zPos);
glVertex3f(200.0f, 200.0f, zPos);
glVertex3f(300.0f, 100.0f, zPos);
    // Bring back buffer to foreground
void SetupPixelFormat(HDC hDC)
    int nPixelFormat;
            sizeof(PIXELFORMATDESCRIPTOR),          //size of structure
            1,                                      //default version
            PFD_DRAW_TO_WINDOW |                    //window drawing support
            PFD_SUPPORT_OPENGL |                    //opengl support
            PFD_DOUBLEBUFFER,                       //double buffering support
            PFD_TYPE_RGBA,                          //RGBA color mode
            32,                                     //32 bit color mode
            0, 0, 0, 0, 0, 0,                       //ignore color bits
            0,                                      //no alpha buffer
            0,                                      //ignore shift bit
            0,                                      //no accumulation buffer
            0, 0, 0, 0,                             //ignore accumulation bits
            16,                                     //16 bit z-buffer size
            0,                                      //no stencil buffer
            0,                                      //no aux buffer
            PFD_MAIN_PLANE,                         //main drawing plane
            0,                                      //reserved
            0, 0, 0 };                              //layer masks ignored
    nPixelFormat = ChoosePixelFormat(hDC, &pfd);

    SetPixelFormat(hDC, nPixelFormat, &pfd);
void InitOpenGL()

GLint iViewport[4];
    glGetIntegerv( GL_VIEWPORT, iViewport );
glViewport(0, 0, iViewport[2], iViewport[3]);
    glOrtho( iViewport[0], iViewport[0]+iViewport[2], iViewport[1], iViewport[1]+iViewport[3], -100.0f, 100.0f );
//glPolygonMode(GL_FRONT, GL_FILL);
glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
/*      Windows Event Procedure Handler */
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
    //      Rendering and Device Context variables are declared here.
    static HGLRC hRC;
    static HDC hDC;
    //      Width and Height for the window our robot is to be displayed in.
    int width, height;
            case WM_CREATE: //window being created
                    hDC = GetDC(hwnd);  //get current windows device context
                    g_HDC = hDC;
SetupPixelFormat(hDC); //call our pixel format setup function
                    //      Create rendering context and make it current
                    hRC = wglCreateContext(hDC);
                    wglMakeCurrent(hDC, hRC);
                    return 0;
            case WM_CLOSE:  //window is closing
                    /*      Deselect rendering context and delete it*/
                    wglMakeCurrent(hDC, NULL);
                    /*      Send quit message to queue*/
                    return 0;
            case WM_SIZE:
                    /*      Retrieve width and height*/
                    height = HIWORD(lParam);
                    width = LOWORD(lParam);
                    /*      Don't want a divide by 0*/
                    if (height == 0)
                            height = 1;
                    /*      Reset the viewport to new dimensions*/
                    glViewport(0, 0, width, height);
                    /*      Set current Matrix to projection and load in the orthographic matrix*/
                    //glLoadIdentity(); //reset projection matrix
                    //glMatrixMode(GL_MODELVIEW); //set modelview matrix
                    //glLoadIdentity(); //reset modelview matrix
                    return 0;
    return (DefWindowProc(hwnd, message, wParam, lParam));
int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
// Getting rid of unused variable warnings.
    WNDCLASSEX windowClass;         //window class
    HWND    hwnd;                   //window handle
    MSG     msg = MSG();            //message
    bool    done;                   //flag for completion of app
    DWORD   dwExStyle;              //window extended style
    DWORD   dwStyle;                //window style
    RECT    windowRect;
    /*      Screen/display attributes*/
    int width = 2880;
    int height = 1800;
    int bits = 32;
    windowRect.left =(long)0;               //set left value to 0
    windowRect.right =(long)width; //set right value to requested width =(long)0;                //set top value to 0
    windowRect.bottom =(long)height; //set bottom value to requested height
    /*      Fill out the window class structure*/
    windowClass.cbSize              = sizeof(WNDCLASSEX);               = CS_HREDRAW | CS_VREDRAW;
    windowClass.lpfnWndProc         = WndProc;
    windowClass.cbClsExtra          = 0;
    windowClass.cbWndExtra          = 0;
    windowClass.hInstance           = hInstance;
    windowClass.hIcon               = LoadIcon(NULL, IDI_APPLICATION);
    windowClass.hCursor             = LoadCursor(NULL, IDC_ARROW);
    windowClass.hbrBackground       = NULL;
    windowClass.lpszMenuName        = NULL;
    windowClass.lpszClassName       = "MyClass";
    windowClass.hIconSm             = LoadIcon(NULL, IDI_WINLOGO);
    /*      Register window class*/
    if (!RegisterClassEx(&windowClass))
            return 0;
    /*      Check if fullscreen is on*/
    if (fullScreen)
        DEVMODE dmScreenSettings;
        memset(&dmScreenSettings, 0, sizeof(dmScreenSettings));
        dmScreenSettings.dmSize = sizeof(dmScreenSettings);
        dmScreenSettings.dmPelsWidth = width;   //screen width
        dmScreenSettings.dmPelsHeight = height; //screen height
        dmScreenSettings.dmBitsPerPel = bits;   //bits per pixel
        dmScreenSettings.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;
        if( ChangeDisplaySettings(&dmScreenSettings, CDS_FULLSCREEN != DISP_CHANGE_SUCCESSFUL) )
            /*      Setting display mode failed, switch to windowed*/
            MessageBox(NULL, "Display mode failed", NULL, MB_OK);
            fullScreen = false;
    /*      Check if fullscreen is still on*/
    if (fullScreen)
        dwExStyle = WS_EX_APPWINDOW;    // window extended style
        dwStyle = WS_POPUP;             // windows style
        ShowCursor(FALSE);              // hide mouse pointer
        dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE; //window extended style
        dwStyle = WS_OVERLAPPEDWINDOW;                  //windows style
    AdjustWindowRectEx(&windowRect, dwStyle, FALSE, dwExStyle);
    /*      Class registerd, so now create our window*/
    hwnd = CreateWindowEx(NULL, "MyClass", //class name
"2D_Project", //app name
dwStyle |
0, 0, //x and y coords
windowRect.right - windowRect.left,
windowRect.bottom -, //width, height
NULL, //handle to parent
NULL, //handle to menu
hInstance, //application instance
NULL); //no xtra params
    /*      Check if window creation failed (hwnd = null ?)*/
    if (!hwnd)
return 0;
    ShowWindow(hwnd, SW_SHOW);      //display window
    UpdateWindow(hwnd);             //update window
    done = false;   //initialize loop condition variable
    /*      Main message loop*/
    while (!done)
        PeekMessage(&msg, hwnd, NULL, NULL, PM_REMOVE);
        if (msg.message == WM_QUIT)     //did we receive a quit message?
done = true;
    if (fullScreen)
        ChangeDisplaySettings(NULL, 0);
    return msg.wParam;

Share this post

Link to post
Share on other sites
I tried using <code></code>, but that didn't seem to do the trick. I can't seem to find the tags you're referring to. If you'll show me, I'll be more than happy to add the tags.

I thought the alpha channel was the other way around? Higher value for higher transparency. I haven't enabled GL_BLEND, so that shouldn't be an issue anyway, correct? I tried it with a 1, and I've verified glDisable(GL_BLEND) doesn't help either.

The only thing I see right now is a blue screen (the clear color). On occasion I can see red, but its not what I expect it to be in terms of size, then I keep messing around with code/values and lose it again... I feel like my ortho setup or camera knowledge is lacking somewher....

Share this post

Link to post
Share on other sites
WHAAAAT? That's really frustrating. I wonder if it has something to do with my machine. I'll try it on another one. I'm currently trying it on a dual booted macbook pro retina. Maybe apple's drivers aren't up to par or something...?

Share this post

Link to post
Share on other sites
Your screenshot gave me an idea.

Ok, I tried using

glVertex3f(0.0f, 200.0f, zPos);
glVertex3f(1600.0f, 900.0f, zPos);
glVertex3f(2800.0f, 200.0f, zPos);

because I have a 2800x1600 display. That way I had a better chance of seeing the triangle, since it would be larger, and I would expect to see the tip of the top be at my center screen, and bottom edges meet properly near the bottom edge of the screen. What I actually see (I'd post a screenshot if I knew the capture button...) is that the triangle tip is appearing roughly in the bottom right quadrant of my screen. Somewhere I must be getting bad values for screen size/viewport size/resolution/whatever.

Share this post

Link to post
Share on other sites
Also of note is that the thumbnail image of the program on my taskbar appears to be correct (maybe slightly off, but certainly different than what the fullscreen image is showing... A fullscreen issue then?

Share this post

Link to post
Share on other sites

The triangle appears where I'd expect it on my computer based on your projection matrix, vertex data and the screen resolution I am running. Try setting your projection matrix to identity (i.e. comment out the gOrtho line in InitOpenGL) and change your polygon draw calls to the following:


glVertex3f(-1.0f, -1.0f, 0);
glVertex3f(1.0f, -1.0f, 0);
glVertex3f(0.0f, 1.0f, 0);

You should see a big red triangle covering the entire screen (regardless of resolution) like this:

Share this post

Link to post
Share on other sites
Doing that, I get a triangle with top at center screen, and bottom corners on the bottom of the screen at 1/4 and 3/4 screen width. The thumbnail image appears to have the triangle positioned such that the bottom left corner is at the bottom left of the image (as if at 0,0), top at (1/3 width, 2/3 height), and the bottom right corner at (2/3 width, 0). I'm still attempting to get this going on another machine too.....

Share this post

Link to post
Share on other sites
Ok, I just verified that everything is fine on another machine. I can only assume the issue has to do with apple's retina display tech. I know they have some kind of new resolution independence code that messes with how the drawing for the new display works. I won't claim to fully understand it, but it must be something to do with it. Their windows drivers must be doing something similar and keeping me from seeing what I expect to see.

The issue only appears in fullscreen mode. Development on this macbook will have to happen in windowed mode. If anyone has a solution, or even explanation, that would be great.

Thanks a bunch for your help GeneralQuery! Edited by fstim82

Share this post

Link to post
Share on other sites

Last I checked when researching some Wordpress graphics was that the retina technology takes an image with double the resolution (200% of the original) and reduces it, so you have more pixels per inch (I guess that would mean 4 pixels in the space 1 pixel normally takes up).

Share this post

Link to post
Share on other sites

Oh, I forgot to mention. Re: code tags. The correct usage is using square brackets rather than angle brackets, i.e.:



[code]type your code here[/code]

I wouldn't worry so much about it for your OP but it's useful to keep in mind for future posts as people with short attention spans (such as myself!) tend to zone out and hit the back button when confronted with a wall of unformatted code wink.png

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Similar Content

    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
    • By dpadam450
      I have this code below in both my vertex and fragment shader, however when I request glGetUniformLocation("Lights[0].diffuse") or "Lights[0].attenuation", it returns -1. It will only give me a valid uniform location if I actually use the diffuse/attenuation variables in the VERTEX shader. Because I use position in the vertex shader, it always returns a valid uniform location. I've read that I can share uniforms across both vertex and fragment, but I'm confused what this is even compiling to if this is the case.
      #define NUM_LIGHTS 2
      struct Light
          vec3 position;
          vec3 diffuse;
          float attenuation;
      uniform Light Lights[NUM_LIGHTS];
    • By pr033r
      I have a Bachelor project on topic "Implenet 3D Boid's algorithm in OpenGL". All OpenGL issues works fine for me, all rendering etc. But when I started implement the boid's algorithm it was getting worse and worse. I read article ( inspirate from another code (here: but it still doesn't work like in tutorials and videos. For example the main problem: when I apply Cohesion (one of three main laws of boids) it makes some "cycling knot". Second, when some flock touch to another it scary change the coordination or respawn in origin (x: 0, y:0. z:0). Just some streng things. 
      I followed many tutorials, change a try everything but it isn't so smooth, without lags like in another videos. I really need your help. 
      My code (optimalizing branch):
      Exe file (if you want to look) and models folder (for those who will download the sources):
      Thanks for any help...

    • By Andrija
      I am currently trying to implement shadow mapping into my project , but although i can render my depth map to the screen and it looks okay , when i sample it with shadowCoords there is no shadow.
      Here is my light space matrix calculation
      mat4x4 lightViewMatrix; vec3 sun_pos = {SUN_OFFSET * the_sun->direction[0], SUN_OFFSET * the_sun->direction[1], SUN_OFFSET * the_sun->direction[2]}; mat4x4_look_at(lightViewMatrix,sun_pos,player->pos,up); mat4x4_mul(lightSpaceMatrix,lightProjMatrix,lightViewMatrix); I will tweak the values for the size and frustum of the shadow map, but for now i just want to draw shadows around the player position
      the_sun->direction is a normalized vector so i multiply it by a constant to get the position.
      player->pos is the camera position in world space
      the light projection matrix is calculated like this:
      mat4x4_ortho(lightProjMatrix,-SHADOW_FAR,SHADOW_FAR,-SHADOW_FAR,SHADOW_FAR,NEAR,SHADOW_FAR); Shadow vertex shader:
      uniform mat4 light_space_matrix; void main() { gl_Position = light_space_matrix * transfMatrix * vec4(position, 1.0f); } Shadow fragment shader:
      out float fragDepth; void main() { fragDepth = gl_FragCoord.z; } I am using deferred rendering so i have all my world positions in the g_positions buffer
      My shadow calculation in the deferred fragment shader:
      float get_shadow_fac(vec4 light_space_pos) { vec3 shadow_coords = / light_space_pos.w; shadow_coords = shadow_coords * 0.5 + 0.5; float closest_depth = texture(shadow_map, shadow_coords.xy).r; float current_depth = shadow_coords.z; float shadow_fac = 1.0; if(closest_depth < current_depth) shadow_fac = 0.5; return shadow_fac; } I call the function like this:
      get_shadow_fac(light_space_matrix * vec4(position,1.0)); Where position is the value i got from sampling the g_position buffer
      Here is my depth texture (i know it will produce low quality shadows but i just want to get it working for now):
      sorry because of the compression , the black smudges are trees ...
      EDIT: Depth texture attachment:
  • Popular Now