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Alpha color doesn't work

Started by Ator Dec 11, 2005 at 12:29 PM 4 replies 500+ views

Original Post

Dec 11, 2005 at 12:29 PM

How do I get 50% transparent polygons? This is my code: (I have overlapped polygons, generated as below) glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA,GL_ONE); glColor4f(1.0, 0.0, 0.0, 0.5); glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); glBegin(GL_POLYGON); glVertex2f(0.0, 0.0); glVertex2f(0.0, 1.0); glVertex2f(1.0, 0.0); glEnd(); glDisable(GL_BLEND); Kind Regards Andreas

nts

Dec 11, 2005 at 2:01 PM

try

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

Also make sure you sort and render your polygons from back to front.

HTH

Ator

Dec 12, 2005 at 5:57 AM

Quote:
Original post by nts
try
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
Also make sure you sort and render your polygons from back to front.

HTH

What do you mean by sort? Sorting regarding what?

/ Andreas

rapunzel

Dec 12, 2005 at 6:04 AM

sort them regarding to their depth. means you should draw the polygon that is most far away first, then the one that is second most far away and so on ...

pauls_1979

Dec 12, 2005 at 6:06 AM

You will need to sort you primitives in order of depth so that those fursthest from the screen are rendered first. Otherwise when the blend operations are performed chances are the z-buffer will contain incorrect values.

Ator

Dec 12, 2005 at 6:15 AM

Quote:
Original post by rapunzel
sort them regarding to their depth. means you should draw the polygon that is most far away first, then the one that is second most far away and so on ...

My code above doesn't render 3D-polygons.

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