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Thread: Frames Overlap

  1. #1
    Junior Member Newbie
    Join Date
    Jan 2007

    Frames Overlap

    Hello guys,
    I m newcomer to OpenGL and so far I have learned on how to use GlDrawpixels(...). I succeeded in rendering 1 color (using GL_LUMINANCE). However, when I used GL_RGB for 256color, the animation frames overlap each other. It is weird because it worked fine for 1-color. Can someone give me any hint whats going on? Here is a bit of mycode.

    Code :
     #include <GL/glut.h>
    #include <GL/gl.h>
    #include <math.h>		
    #include <string.h>		
    #define NS_WINSIZE 512
    const float PI=3.14159265358979;
    float XPoint(float,float, float,float, float,float);
    float YPoint(float,float, float,float, float,float);
    void fractal(float,float,int,const float);
    unsigned char img1[NS_WINSIZE * NS_WINSIZE][3];
    void display()
    	for (unsigned int i = 0; i < 48; i++)
    		memset(img1,0, NS_WINSIZE * NS_WINSIZE);
    int main(int argc, char** argv){
    	glutInit(&amp;argc, argv);
    	glutInitWindowSize(NS_WINSIZE, NS_WINSIZE);
    	glutCreateWindow("Fractal Viewer");
    	return 0;
    float XPoint(float xc,float yc, float theta,float scale, float x,float y){
      return ((x*cos(theta)-y*sin(theta))*scale+xc);
    float YPoint(float xc,float yc, float theta,float scale, float x,float y){
      return ((x*sin(theta)+y*cos(theta))*scale+yc);
    void fractal(float x, float y, int depth, const float ang) {
      if (depth==0) {
    	int xc,yc;
    	xc = int( (x-(-2)) * NS_WINSIZE/4);
    	yc = int( (y-(-2)) * NS_WINSIZE/4);
      } else {
    The colors blend works well. The only problem is overlapping frames.

  2. #2
    Junior Member Newbie
    Join Date
    Jan 2007

    Re: Frames Overlap

    Forgot to mention that the frames overlap while the they going down of Y-axis (which means animation keep going down instead of sitting at a same place until it ends).

  3. #3
    Intern Contributor
    Join Date
    Mar 2006

    Re: Frames Overlap

    I tried to run your code and it froze my system, then I realized it was just taking a really long time to complete

    Interesting... what fractal is that? Anything famous?

    When I get into a pickle like this, I usually sprinkle a few break points around in my code and run the debugger, so I can see the flow and what's happening to my data as she runs.

  4. #4
    Junior Member Newbie
    Join Date
    Jan 2007

    Re: Frames Overlap

    Your imgl array is not well allocated.
    First, it is a bi-dimensionnal array, while glDrawPixels expects a one-dimension pointer.
    You should have imgl be allocated this way:

    unsigned char img1[NS_WINSIZE * NS_WINSIZE * 3];

    The memset looks like a waste of time, because you define all the values of the array anyway, and I don't see any dependency between pixels in your fractal computation. So it can be called only once outside of the loop, it not at all. But I may miss something.
    Anyway, my point is that once you moved to a single dimensioned array, then your memset line should look like this:

    memset(img1,0, NS_WINSIZE * NS_WINSIZE * 3);

    And finally, in the fractal() function, you should assign values this way:

    img1[(NS_WINSIZE*yc+xc)*3 + 1]=51;
    img1[(NS_WINSIZE*yc+xc)*3 + 2]=153;

    Also, you have to know that glDrawPixels is usually optimized for 32-bit format, rather than 24-bit, so you may consider using GL_RGBA or GL_BGRA instead, replacing 3 by 4 and leaving the alpha value as 255
    Michael Boccara
    Graphtech Computer Systems ltd.
    Herzliya, Israel

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