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04-29-24 08:09 PM |
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| 0 users currently in Computing | 1 guest |
| Main - Computing - Seeing through solid objects in OpenGL | New thread | New reply |
| HyperHacker |
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... Level: 73 Posts: 237/1220 EXP: 3367698 Next: 118170 Since: 03-25-07 From: no Last post: 6094 days Last view: 6078 days |
Having some trouble with alpha blending in OpenGL. Here there is an object in front of this wall, but I've switched it to wireframe so we can see the wall behind it. The object is alpha-blended, but the wall is not.
Now when I switch wireframe off, we can see the object, but for some reason in the areas that are transparent, we see right through the wall behind it too! 
So, uh... wtf? |
| Cellar Dweller |
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 Snifit Level: 39 Posts: 17/287 EXP: 385291 Next: 19480 Since: 02-19-07 From: Arkansas Last post: 4055 days Last view: 3222 days |
Are you making sure to draw the alpha blended objects last? It looks like you are drawing the alpha blended object before drawing the wall. This causes the depth buffer to be set at the depth of the alpha blended object, and then the wall fails the depth test and is not shown. |
| HyperHacker |
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... Level: 73 Posts: 246/1220 EXP: 3367698 Next: 118170 Since: 03-25-07 From: no Last post: 6094 days Last view: 6078 days |
Hm, I thought having depth testing on would take care of that. Does that mean if I have one blended object in front of another, and any object behind that, they won't show up correctly?
Anyway thanks, that got it. Now I just need to figure out the damn format of these textures. Seems to be 4 bits of red, green, blue and alpha, but I haven't got them showing up correctly yet...  |
| Cellar Dweller |
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Snifit Level: 39 Posts: 18/287 EXP: 385291 Next: 19480 Since: 02-19-07 From: Arkansas Last post: 4055 days Last view: 3222 days |
Multiple alpha blended objects will show up correctly if they are drawn back to front. I don't think its worth the trouble to do that for a N64 game viewer/editor, as alpha blended objects seem to be used sparingly, and the N64 has the same alpha blending limitation.
This is all because after an alpha blended object is drawn, the renderer doesn't have enough information to blend another object in behind it. |
| GuyPerfect |
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 Paratroopa Level: 30 Posts: 12/155 EXP: 152641 Next: 13228 Since: 03-14-07 Last post: 6048 days Last view: 5997 days |
It's important to rememebr that blending is NOT the same as transparency; it's a technique used to simulate transparency. A solid pixel takes the COLOR of its source and destination pixels in the buffer, and depth testing would make any pixel drawn behind it, well... not drawn to the buffer. I hope that makes sense.
But like Cellar Dweller mentioned, draw everything back-to-front when alpha blending in order to adequately display objects that need to appear transparent. |
| HyperHacker |
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... Level: 73 Posts: 259/1220 EXP: 3367698 Next: 118170 Since: 03-25-07 From: no Last post: 6094 days Last view: 6078 days |
OK, thanks. Now to figure out how I'm going to implement that. Rainbow Road is completely blended, and eventually I'm going to want to do things not related to N64 games... |
| BMF54123 |
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 Buzzy Beetle Level: 44 Posts: 168/375 EXP: 575456 Next: 35829 Since: 02-19-07 From: [citation needed] Last post: 6089 days Last view: 6089 days |
So, does all this explain why overlapping translucent objects in N64 games seem to be drawn in the wrong order (i.e. you can see Rainbow Road's star railing clearly through the underside of the road)? ____________________ [citation needed] |
| GuyPerfect |
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Paratroopa Level: 30 Posts: 18/155 EXP: 152641 Next: 13228 Since: 03-14-07 Last post: 6048 days Last view: 5997 days |
I think Rainbow Road's star rail is actually drawn to the buffer with depth testing disabled... or maybe the track portion is... or maybe the depth buffer is cleared between the two... There's any number of explinations, but it's depth-test related instead of blend related.
Ah, the intricacies of 3D graphical development. It's one of the only forms of programming that's like an art. Some people become very proficient with graphical tricks, while others still think that the objects are solid... |
| Main - Computing - Seeing through solid objects in OpenGL | New thread | New reply |
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