Thread: How to Rotate a line?

I want to point out that void main is undefined. You should use int main instead.

Originally Posted by hariharan

@elysia

I can see your hatred towards void main from your siggy , but I don't have a need to define the return type for main() in my program.

You do no seem to understand. Whether or not you need to return something is irrelevant. Void main is undefined behavior and should not compile at all. Unfortunately, it does compile, but it is still undefined and very, very bad. So don't use it. Use int main.

I'm working with some rotating rim spokes for your car's wheels.

You should have some "bad" low-rider wheels later this evening.

It's not terribly sophisticated, (no math involved), but it might work.

Code:

#include <graphics.h>

/* 
line(x, y, x+cos(degrees)*length, y+sin(degrees)*length);
x, and y would be the point around which to rotate. In C you also need to 
convert degrees to radians tho.

Can we add spokes/rims to the wheels, and show them rotating?
Add a black line, same xy's, that chases the blue one, deleting them.
*/

int main()
{

   int i, msec;  //milliseconds used by delay()
   int gd=DETECT, gm, errorcode;  //int gd=DETECT,gm;

   /* 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: &#37;s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);                                      /* return with error code */
   }

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

      msec = 30;
      line(i+20, 160, i+20, 164);      //6 o'clock line
      delay(msec);                    //after a delay
      setcolor(0);                    //erase it
      line(i+20, 160, i+20, 164); 
 
      setcolor(3);
      line(i+20, 160, i+10, 160);     //9 o'clock 
      delay(msec);
      setcolor(0);
      line(i+20, 160, i+10, 160);

      setcolor(3);
      line(i+20, 160, i+20, 156);     //12 o'clock
      delay(msec);
      setcolor(0);
      line(i+20, 160, i+20, 156);

      setcolor(3); 
      line(i+20, 160, i+30, 160);     //3 o'clock
      //delay(msec);

      delay(msec);  //was 25
      cleardevice();                  //3 o'clock erased here
   }

   closegraph();
   return 0;
}

The "turning wheel spokes", could have spokes at 2, 4, 8, & 10 o'clock positions, instead, or have them both, to double up on the realism.

A small circle in the center of each wheel could serve as a visual wheel hub, when the spokes would
stop at the circumference of the hub, instead of going on to the center of the wheel (which looks a bit cartoony, imo). Edit: tried this, and it
didn't look good. Went with more spokes, and a sliding scale of "visibility", below. That worked very well.

I played around with the timing a lot, the above looks good on a P3, but it may need to be adjusted for other cpu's.

This is the best rear wheel I could come up with, consistent with your design. I left the front wheel unchanged for comparison.

You're cruisin' now!

Code:

#include <graphics.h>
/* 
line(x, y, x+cos(degrees)*length, y+sin(degrees)*length);
x, and y would be the point around which to rotate. In C you also need to 
convert degrees to radians tho.

I didn't use the above info.
*/
int main()
{
   int i, msec;  //milliseconds used by delay()
   int gd=DETECT, gm, errorcode;  //int gd=DETECT,gm;
   //initgraph(&gd,&gm,"");      //for my system
   initgraph(&gd,&gm,"e:\\lab\\tc\\bgi");

   /* check if it loaded OK */
   errorcode = graphresult();
   if (errorcode != grOk) {  /* an error occurred */ 
      printf("Graphics error: &#37;s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);             /* return with error code */
   }

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

	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+20,160,12);			//Wheel depth
	circle(i+80,160,10);			//WHEEL2

        msec = 10;
	line(i+20, 160, i+20, 164);     	//6 o'clock line
	//delay(msec);				   //after a delay
        if(i % 3 == 0) {
           setcolor(0);				//erase it
 	   line(i+20, 160, i+20, 164); 
        }

	setcolor(3);
	line(i+20, 160, i+16, 163);		//8 o'clock line
	//delay(msec);				//after a delay
	if(i % 4 == 0) {
		setcolor(0);			//erase it
		line(i+20, 160, i+16, 163); 
	} 
        setcolor(3);
	line(i+20, 160, i+10, 160);		//9 o'clock 
	//delay(msec);
	if(i % 5 == 0) {
		setcolor(0);
		line(i+20, 160, i+10, 160);
	}
	setcolor(3);
	line(i+20, 160, i+15, 158);		//10 o'clock 
	//delay(msec);
	if(i % 6 == 0) {
		setcolor(0);
		line(i+20, 160, i+15, 158);
	}
	setcolor(3);
	line(i+20, 160, i+20, 156);		//12 o'clock
	delay(msec);
	if(i % 7 == 0) {
		setcolor(0);
		line(i+20, 160, i+20, 156);
	}
	setcolor(3);
	line(i+20, 160, i+25, 158);		//2 o'clock
	delay(msec);
	if(i % 8 == 0) {
		setcolor(0);
		line(i+20, 160, i+25, 158);
	}
	setcolor(3); 
	line(i+20, 160, i+30, 160);		//3 o'clock
	delay(msec);
	if(i % 9 == 0) {
		setcolor(0);
		line(i+20, 160, i+30, 160);
	}
	setcolor(3); 
	line(i+20, 160, i+25, 162);		//4 o'clock
	delay(msec);
	if(i % 10 == 0) {
		setcolor(0);
		line(i+20, 160, i+25, 162);
	}
	delay(msec);				//was 25
	cleardevice();				//last o'clock line erased here
     }

      closegraph();
      return 0;
}

The delay before erasing gave way to a better looking scheme involving the a sliding scale use of mod on i, to determine if a line should be erased.

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:

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

int main()
{

   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: &#37;s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);                                      /* return with error code */
   }
    
   // Some new variables
   int spokes, degrees = 0, speed = 3, angle;
   unsigned start_time;

   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;
}

Code:

      delay(17-(clock()-start_time));

Lets hope:
1. clock() returns a time compatible with delay.
2. That clock()-starttime isn't greater than 17.

--
Mats

Actually, the above code runs in DOS - albeit emulated inside Windows.

--
Mats

Originally Posted by mike_g

Oh, I though graphics.h was a windows thing. Guess not. Well I supposed if you ran it in DOSbox on Linux it it would be a bit screwed up then.

Probably not, it's not dependant on the underlaying OS architecture, it's the implementation of "clock" that I'm concerned with - I'm just pointing out that "clock()" may not return a number of milliseconds. Unfortunately it gets a bit difficult to fix if you want to make it fully portable.

--
Mats