Help Drawing Lines

More info!

What platform, what language, what API etc etc. There are 2353 ways to draw lines so help us out in knowning which one you want.

It's C#, using GDI+.

Second hit on Google.

Also, you tend not to specify lines as position and direction, more start and end points. You can calculate the end point from an angle with some basic trigonometry though.

EDIT: With GDI in C++, the function is LineTo. I imagine the C# / GDI+ equivalent will be similar and easy to find on MSDN / Google.

The problem is not to draw the line, but to find the end points...
I know it's really a simple solution but I just can't remember the math of that.

Well, if you know the X coordinate of the target point (the edge of the rectangle), then you can work out the Y coordinate from the angle with:
y = x * tan(angle)

you mean dy=dx*tan(alpha) ?
anyway i don't have the x coordinate.
I've a rectangle with its (left,top) and (right, bottom), i've the center of the rectangle. I need to draw 24 lines, one every 15 degrees, from the center to the edge of the rectangle.

i can do:
line(cx,cy,cx+cos(alpha),cy+sin(alpha))
it will make the lines which i need but they won't reach the edges of the rectangle but the perimeter of the surrounded circle. i need them to reach the edges of the rectangle.

If the math is over your head you could try masking. I don't know if GDI+ is capable of that though. If GDI+ has no masking functions you could manually plot your line with pixels and check to see if your pixel is inside the rectangle.

The dimensions and the position of the rectangle is not static.

Quote:

Original post by khdani you mean dy=dx*tan(alpha) ? anyway i don't have the x coordinate. I've a rectangle with its (left,top) and (right, bottom), i've the center of the rectangle. I need to draw 24 lines, one every 15 degrees, from the center to the edge of the rectangle. i can do: line(cx,cy,cx+cos(alpha),cy+sin(alpha)) it will make the lines which i need but they won't reach the edges of the rectangle but the perimeter of the surrounded circle. i need them to reach the edges of the rectangle.

C++ code, but should convert to C# easily enough:
That's just a very rough stab at it, I don't have time to properly test it just now. You'll also want to convert all angles to radians.

Essentially you know the X or Y value and the angle, so you can work out the missing value.

Thank you Steve!
I'll try your code.
I've managed to draw it for 0-90 degrees, but your code looks simpler.

That's C++ code...try porting it in C#

void Graphic::FillRect(RECT Rect, float radinc)
{
POINT Pt;
POINT Center;
float alfa = 0.0f;
float archeight = atan(( (Rect.bottom-Rect.top)/2 ) / ( (Rect.right-Rect.left)/2));

//point at the center of the rectangle
Center.x = LONG(Rect.left + ((Rect.right-Rect.left)/2));
Center.y = LONG(Rect.top + ((Rect.bottom-Rect.top)/2));

Pt.x = Rect.right;
for (; alfa < archeight; alfa += radinc)
{
Pt.y = LONG(floor(tan(alfa) * Rect.right));
Graphic.DrawLine(Center, Pt);
}
Pt.y = Rect.top;
for (; alfa < (Math.Pi-archeight); alfa += radinc)
{
Pt.x = LONG(floor(Rect.top / tan(alfa)));
Graphic.DrawLine(Center, Pt);
}
Pt.x = Rect.left;
for (; alfa < (Math.Pi+archeight); alfa += radinc)
{
Pt.x = LONG(floor(Rect.top / tan(alfa)));
Graphic.DrawLine(Center, Pt);
}
Pt.y = Rect.bottom;
for (; alfa < ((2*Math.Pi)-archeight); alfa += radinc)
{
Pt.x = LONG(floor(tan(alfa) * Rect.right));
Graphic.DrawLine(Center, Pt);
}
Pt.x = Rect.right;
for (; alfa < (2*Math.Pi); alfa += radinc)
{
Pt.y = LONG(floor(tan(alfa) * Rect.right));
Graphic.DrawLine(Center, Pt);
}
}

radinc is the angular increment (in radians!)

well...I'm a bit late...use the code you like the most. Good work!

Thank you ZeroMemory!