Blend Order

BlitzMax Forums/OpenGL Module/Blend Order

BLaBZ

(Posted 2012) [#1]

My texture triangle blend order seems to only be correct when I'm below the ground plane

-Above the ground plane

-Below the ground plane

glMatrixMode(GL_MODELVIEW)

			Local modelView:Float[16]
		
			glPushMatrix
			
			glTranslatef Particle.x,Particle.y,Particle.z
			
	
			glGetFloatv(GL_MODELVIEW_MATRIX,modelView)
		
			For Local i:Int = 0 To 2 
				For Local j:Int = 0 To 2
					If i = j
						modelview[i*4+j] = 1.0
					Else
						modelview[i*4+j] = 0.0
					EndIf 
				Next
			Next
			

			glLoadMatrixf(modelView)
			
	
			
			glColor4f 0.2,0.2,0.2,Particle.Alpha
			glRotatef Particle.Rotation, 0.0,0.0,1.0
			glBegin(GL_TRIANGLE_STRIP)										' Build Quad From A Triangle Strip
				glTexCoord2f(1,1); glVertex3f(Particle.size,Particle.size,0)					' Top Right
				glTexCoord2f(0,1); glVertex3f(-Particle.size,Particle.size,0)					' Top Left
				glTexCoord2f(1,0); glVertex3f(Particle.size,-Particle.size,0)					' Bottom Right
				glTexCoord2f(0,0); glVertex3f(-Particle.size,-Particle.size,0)					' Bottom Left
			glEnd()	

			glPopMatrix

If I translate after I set the current matrix the blending appears correct but the position isn't.

Any help is really appreciated

-Thanks

BLaBZ

(Posted 2012) [#2]

It seems to work when the view angle is "up" but not "down"

BLaBZ

(Posted 2012) [#3]

Ok found the solution

had to call glDisable(GL_DEPTH_TEST)

"The Z buffer doesn't work as you might hope for transparent polygons.
The problem is that the Z buffer prevents OpenGL from drawing pixels that are behind things that have already been drawn. Generally, that's pretty convenient, but when the thing in front is translucent, you need to see the things that are behind it."

BLaBZ

(Posted 2012) [#4]

Maybe I was wrong again...

Apparently you have to "Depth Sort"

My rendering order was causing the issue.

jkrankie

(Posted 2012) [#5]

Remember to disable gl_Alpha_test if you want to use alpha values less than 0.5ish.

Cheers
Charlie