How to Rotate a line?

@mike_g : You've made my day pal! thank you so much :)

@matsp : Could you please explain your point in layman's view? I'm not getting much

Quote:

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Originally Posted by mike_g

Well heres my solution. Not sure if it will actually work as I never used graphics.h, and haven't tested it. But anyway:

Code:

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#include <graphics.h>
#include <math.h>
#include <time.h>
#define DEG_TO_RAD 0.0174532925

int main()
{

    // Some new variables
  int spokes, degrees = 0, speed = 3, angle;
  unsigned start_time;

  int i;
  int gd=DETECT, gm, errorcode;

  /* what I use: initgraph(&gd,&gm,""); */
  initgraph(&gd,&gm,"e:\\lab\\tc\\bgi");
 
  /* check if it loaded OK */
  errorcode = graphresult();
  if (errorcode != grOk) {                /* an error occurred */
      printf("Graphics error: %s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);                                      /* return with error code */
  }
   
 

  for(i=100;i<400;i++)   
  {
      start_time = clock();     

      setcolor(3);
      line(i,100,i+15,85);                        //RISING LINE
      line(i+15,85,i+70,85);                //ST.LINE AT TOP
      line(i+70,85,i+100,100);            //FALLING LINE
      rectangle(i+100,150,i,100);          //BODY
      rectangle(i+10,130,i+30,110);  //WINDOW1
      rectangle(i+40,130,i+60,110);  //WINDOW2
      rectangle(i+70,130,i+90,110);  //WINDOW3
      circle(i+15,125,5);                      //FACE1
      circle(i+45,125,5);                      //FACE2
      circle(i+75,125,5);                      //FACE3
      circle(i+20,160,10);                    //WHEEL1
      circle(i+80,160,10);                    //WHEEL2
     
      // Draw each spoke 
      for(spokes = 0; spokes < 8; spokes ++) 
      {
          angle = (degrees+spokes*45)*DEG_TO_RAD;
          line(i+20, 160, i+20+cos(angle)*10, 160+sin(angle)*10); 
      }
      // Rotate
      if((degrees+=speed) > 359) degrees -= 360;
     
      // Run at ~60fps
      if(clock()-start_time < 17) delay(17-(clock()-start_time)); 
      cleardevice();                 
  }

  closegraph();
  return 0;
}

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It runs in Turbo C with the changes I made above - very minor. I love the way you've done this Mike, but the spokes stick 1/4 of the way outside the wheel, *4 instead of 10 fixes that, but then some spokes are too short (an aspect ratio problem maybe?), and the spokes appear "spazzy" and bunched up together around the 6 o'clock and 12 o'clock, position. Even with much longer delay times, I couldn't see spokes ever appearing at the 9 o'clock or 3 o'clock, positions.

I do love how compact it is. Much more practical than mine, if I could get it to behave itself! :D

The function "clock()" is not defined to return milliseconds. It is defined to return "a count of clock-ticks" - how big a clock-tick is depends on the implementation - you can find out how many clock-ticks per second"CLOCKS_PER_SEC", but the code from Mike_g is relying specifically on the tick-size being compatible with the function delay, which takes milleseconds as input.

In this case, it's no big deal - the code will probably run only in DOS (because it uses Turbo C specific code, including the "delay" function itself) - but in general, it's a good idea to NOT rely on how large the unit of a clock-tick is - it could be a microsecond (1000000 ticks per second) or it could be 10 ms (100 ticks per second), or something else (147138 ticks per second, perhaps?) - it all depends on for example what timing hardware there is on the machine - it may have a timer that runs at 1/10 of a 1.47138MHz crystal - then that's what you get!

Of course, if you feed delay with a number that is 1000 times larger than you want, then you get a very long delay, and if you feed delay with a number much smaller than the correct value, then you don't get a long enough delay.

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Mats

Adak: I guess I thought the radius was 10 pixels when it was the diameter. Like I said I couldent test it to see what it came out like. I imagine the main reason it looks so bad is because the wheels are so tiny, it should look better on bigger wheels. I think the pixels sticking out problem has to do with the way that the circle is drawn. Its likely that graphics.h draws Bresenham circles because its a fast and accurate algorithm. However the curvature ends up slightly different to a circle drawn using sin and cos.

matsp: I usually use SDL_GetTicks(), maybe graphics.h has a method for getting the time in millisecs too? and yeah clock() seems to suck.

Erm.. Actually ignore that stuff I was babbling about to do with circles. The answer was painfully obvious; the circle needs to have an odd diameter. Otherwise on one half the spokes will end up one pixel too long, or short.

@Mats

Thanks for the explanation dude :)