Thread: Is there an easiest way to rotate a line?

Here's my attempt! but doesn't work, freezes at most and no draws solid lines (no rotation)

Code:

case WM_PAINT:
                while (cntr++ < 180)
		{ 
		DrawLine(hdc, ptCenter, SetPOINT(ptCenter, radius), 255, 128, 128);
		Sleep(2000);
		}
		break;
	
.........


void DrawLine(HDC hdc, POINT ptCenter, POINT coord, int R, int G, int B)
{
	HPEN pen, oldPen;

	pen = CreatePen(PS_SOLID, 2, RGB(255, 0, 0));	
	oldPen = (HPEN)SelectObject(hdc, pen);				

	MoveToEx(hdc, ptCenter.x,ptCenter.y, NULL);		
	LineTo(hdc, coord.x, coord.y);					

	SelectObject(hdc, oldPen); 				
	DeleteDC(hdc);										
}

/* Calculate the line points */
POINT SetPOINT(POINT ptCenter, LONG radius)
{
	const float Deg2Rad = 0.017453292;
	POINT coord;
	static int angle=0;
	float degInRad;

	degInRad = angle*Deg2Rad	   // Convert degrees to radians
	coord.x = ptCenter.x + (cos(degInRad)*(float)radius); // Finds the adjacent value
	coord.y = ptCenter.x - (sin(degInRad)*(float)radius);	// Finds the hypotenuse value
	angle-=5;            // Prepare for the next line position (clockwise direction)

	return coord;
}

Originally Posted by novacain

Is 'cntr' a static? If not it will have also lost scope and may not contain the value you expect.

Regarless of where cntr is declared? would this be valid..

Code:

for(static int cntr=0;cntr<180;cntr++)

ZeroMemory(PS,sizeof(PAINTSTRUCT));

error C2664: 'memset' : cannot convert parameter 1 from 'PAINTSTRUCT' to 'void *'

Code:

void ZeroMemory(
  PVOID Destination, // This expects void pointer, ps doesn't seem to work
  SIZE_T Length 
);

Why should i use ZeroMemory?

Won't the static variable only allow the loop to execute once? Unless the function changes cntr back to 0 at the end. Because once the loop executes the first the the static is initialized, so it will not initialize again. Or am I completely wrong?

[QUOTE=matsp;745011]ps is a struct, so you need the address of operator (&) to make it a pointer to the struct, which is what ZeroMemory uses.

Code:

ZeroMemory(PS,sizeof(PAINTSTRUCT));

was hoping for an example!!

[QUOTE=matsp;745049]

Originally Posted by csonx_p

Yes, it was meant to be - typo - sorry about that:

Code:

ZeroMemory(&PS,sizeof(PAINTSTRUCT));

Although I think I explained what was wrong - you are passing a struct, you need a pointer.

--
Mats

My algorithm leaves lines drawn which defiles my aim of rotating a line. Is there a way i could erase a previous line before drawing a new on on new coordinates?

Originally Posted by matsp

Well, you can do one of two things:
1. "undraw" the previous line by remembering where it used to be drawn (this assumes background is known, since you need to draw that part of the background).
2. Draw the entire surface with whatever was there before the line was drawn.

--
Mats

Both options sounds a little uneasy to me... Is there a function to undraw?

Originally Posted by matsp

then copy the region covered by your drawing [easier if you make it a rectangle covering the extremes of your drawn object], and to "undraw", just draw back what you previously drew.
Mats

I'm sorry for being dumb, how do you copy a window region?

Originally Posted by matsp

BitBlt(), using ROP SRCCOPY, perhaps?

--
Mats

Thanx Mats, will try them.. If you don't mind please look at my SetTimer thread!