Round Buttons

Tuesday Nov 24th 1998 by Chris Maunder

Round Buttons

Round buttons Download sample project and source files

Yes - I know there is already a topic on circular push buttons but they weren't quite what I wanted, so I wrote my own. What I wanted was a button that looked exactly like the normal buttons, but instead I wanted them circular.

First of all I make sure the buttons are circles (and not ellipses) and store the centre and radius of the button. Next I simply make the button owner drawn and draw it like every other owner drwn button, but instead of being able to use nice routines like Draw3dRect, I had to roll my own circle drawing routine which would draw each pixel with the correct colour dependant on the point on the circle I was drawing.

I will not include the full source in this page - it is available for download here. The owner draw part is simple and follows along the lines of any other owner drawn button. The circle drawing routine is a standard algorithm, with the only modification in calculating the pixel colour. Given two colours crBright and crDark, and an angle relative to the x-axis, the colour for a pixel can be calculated using the following.
COLORREF GetColour(double dAngle, COLORREF crBright, COLORREF crDark)
#define Rad2Deg	180.0/3.1415 
#define LIGHT_SOURCE_ANGLE -2.356    // -2.356 radians = -135 degrees, 
                                     // i.e. From the top left of the screen

	ASSERT(dAngle > -3.1416 && dAngle < 3.1416);
	double dAngleDifference = LIGHT_SOURCE_ANGLE - dAngle;

	if (dAngleDifference < -3.1415) dAngleDifference = 6.293 + dAngleDifference;
	else if (dAngleDifference > 3.1415) dAngleDifference = 6.293 - dAngleDifference;

	double Weight = 0.5*(cos(dAngleDifference)+1.0);

	BYTE Red   = (BYTE) (Weight*GetRValue(crBright) + (1.0-Weight)*GetRValue(crDark));
	BYTE Green = (BYTE) (Weight*GetGValue(crBright) + (1.0-Weight)*GetGValue(crDark));
	BYTE Blue  = (BYTE) (Weight*GetBValue(crBright) + (1.0-Weight)*GetBValue(crDark));

	return RGB(Red, Green, Blue);

This is a simple linear interpolation between the two colours based on the cosine of the angle between the light source and the point. Angles are measured from the +ve x-axis (i.e. (1,0) = 0 degrees, (0,1) = 90 degrees ), but remember: positive y points down!

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