Jump to content
  • Advertisement
Sign in to follow this  

Having trouble blending the colors of an anti-alias line, help plz!

This topic is 1865 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts



I recently learned how to render anti-alias lines using the Wu algorithm. All was going well until I decided to change the background color from black to another color, and the results changed to this:




from this:




To solve the problem I tried to alpha blend the resulting pixel, calculated with the Wu algorithm, with the background pixel underneath it. The results did not look any better. So, is there any way to modify the Wu algorithm to take in account the background pixel when calculating the levels of intensity for the new pixel of the anti-alias line? This article( http://www.codeproject.com/Articles/13360/Antialiasing-Wu-Algorithm ) does it successfully but I can't duplicate the results because I have trouble deciphering the source code. Also are there any smoothing techniques that I could use to smooth out the lines? Because if you look at the lines of the black image you will notice a candy cane like effect on some of the lines.


Here is some source code to help under stand what's going on:

if( fabs(delta.x) >= fabs(delta.y) )	// line is more horizontal
		if( p0.x > p1.x )	// process left to right
			SmyVectorF temp = p0;
			p0		= p1;
			p1		= temp;
			delta	= SmyVectorF( p1.x-p0.x, p1.y-p0.y );

		int x0			= (int)floor(p0.x);		// start x
		int x1			= (int)floor(p1.x);		// end x
		float y			= p0.y;
		float gradient	= delta.y / delta.x;	// slope of the line

			for( int x = x0; x < x1; x++ )
				if( x >= 0 && x < w && y >= 0 && y <= h )
				float intensity1	= y-float(floor(y));
				float intensity0	= 1.f-intensity1;
				UNINT pixel					= (UNINT) (floor(y)*w)+x;
				backbuffer->bits[pixel]		= SMYUTI_rgb( UNCHR(red*intensity0), UNCHR(green*intensity0), UNCHR(blue*intensity0) );
				backbuffer->bits[(pixel+=w)]	= SMYUTI_rgb( UNCHR(red*intensity1), UNCHR(green*intensity1), UNCHR(blue*intensity1) );
				y += gradient;
		if( p0.y >= 0 && p0.x >= 0 && p0.y <= h && p0.x <= w )
			backbuffer->bits[int(p0.y)*w+int(p0.x)]	= m_color;	// render start pixel

		if( p1.y >= 0 && p1.x >= 0 && p1.y <= h && p1.x <= w )
			backbuffer->bits[int(p1.y)*w+int(p1.x)]	= m_color;	// render end pixel

Thanks in advance.

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!