Alphablend + Alpha 0.01 + Rect = wtf?
BlitzMax Forums/BlitzMax Programming/Alphablend + Alpha 0.01 + Rect = wtf?
| ||
| Hi there I'm trying to do some nice Movement-Blur with easily replacing the Cls-Command with an alpha-blended, black Drawrect. Well it sounds easier than it is because of a nasty Bug, I can't explain. The Background doesn't really fade away, there always will be a grey area where the image was. Look at my Example-Fading-program: Graphics 800,600,0,60 SetColor 255,255,255 DrawRect 100,100,100,100 WaitKey While Not KeyHit(KEY_ESCAPE) SetColor 0,0,0 SetAlpha 0.01 SetBlend ALPHABLEND DrawRect 100,100,100,100 Flip Wend Why the hell doesn't the white rect disappear? If you set Alpha to 0.1, it's not that hard but still visible and it disturbs the whole effect. If you set Alpha to 0.001, the white Rect keeps completely white. It's just strange. Hope, you can help me. |
| ||
<edit> Ooops, understand now... 'SetGraphicsDriver GLMax2DDriver() Graphics 800,600,0,60 SetColor 255,255,255 DrawRect 100,100,100,100 WaitKey While Not KeyHit(KEY_ESCAPE) SetColor 255,0,0 SetAlpha 0.01 SetBlend ALPHABLEND DrawRect 100,100,100,100 Flip Wend If you still see a white rectangle then uncomment the setgraphicsdriver command and run it again. |
| ||
| Hi, I'm guessing it's because you're running in 16bit mode. If you are you will encounter stuff like this. Try this version it should work in both 16 and 32 bit: Graphics 800,600,0,60 SetColor 255,255,255 DrawRect 100,100,100,100 WaitKey While Not KeyHit(KEY_ESCAPE) SetColor 240,240,240 SetBlend SHADEBLEND DrawRect 100,100,100,100 Flip Wend |
| ||
| Nope, neither tonyg's nor fredborgs's program runs like it should. I see a grey non-fading rect in both examples. :/ And, I'm running with 32 Bit. The error still occurs, if i set 32 Bit in the Graphics-Command. |
| ||
| You are counting on the contens of the backbuffer to be unchanged after a flip. As far as I know you shouldn't. After a flip the contens of the backbuffer is undefined and you should draw everything again. In your case draw it and then cover it by a gradually more and more opaque black retangle. |
| ||
| On my 9800Pro machine they both work as expected unless I set 0.001 then they stay white. On my laptop (S3) the image turns 'grey' as if the first alpha change was applied but then stays the same. Basically, on my laptop I get the same problem, on my desktop it's OK. It has to be a driver issue.... doesn't it? |
| ||
| Or the card itself can't handle something simple like alpha properly... maybe... what's your tech specs? And DocFritz, what are yours? |
| ||
| Possible, if I change the alpha to 0.1 it works as mentioned above. |
| ||
| I've got a Geforce 6800 GT, I don't think that a new card has Problems with simple Alpha-Stuff *g* I count on OpenGL. Or on Max2D. On of them must have an error or something. By the way: Where do I get the new Nvidia OpenGL-Drivers? I don't find them anywhere? |
| ||
| I'll repeat: "After a flip the contens of the backbuffer is undefined and you should draw everything again." Have you tried that? |
| ||
| Hello. @Peter: Try shouting :o) Goodbye. |
| ||
| I'll repeat: "After a flip the contens of the backbuffer is undefined and you should draw everything again." Have you tried that? Hmmm.. so why does 0.1 work as expected (but too fast) while 0.01 stop before the rect is faded completely? Interestingly, if you use other values (e.g. 0.05) the effect gets further but then still stops. |
| ||
| @Peter No, I haven't tried. But it would mean, that I'd have to draw EVERYTHING about 15 times to get a nice Motionblur. And I donÄt want the FPS to fall down just for a little Effect... @tonyg Yeah, it's weird, but there is a system in this anomaly. |
   |