[PATCH] Don't render transparent objects twice

[Philip Taylor]

CRenderer::RenderSubmissions() calls RenderTransparentModels() twice, once before drawing water and once after, so that underwater transparent models will blend properly.

That seems like a terrible idea. We have lots of transparent objects (trees) so it will kill performance; and the overdraw makes transparent objects look different, so when we fix the performance bug all the art will be wrongly calibrated.

Possible temporary solution: don't support transparent objects underwater. Possible better solution: do the overdraw only on models which intersect the water plane. Ideal solution: render transparent objects correctly always (but I don't know how that'd be implemented).

[peter_ym_account]

Single render transparent objects screenshot

[peter_ym_account]

double render transparent objects (current behavior) screenshot

[peter_ym_account]

As Philip reported, and illustrated in the screenshots, transparent objects are twice as opaque when rendered twice. Underwater objects appear to render correctly with only a single post-water render when fancy water is enabled; so maybe the underwater transparency double-rendering is only necessary when fancy water is disabled.

[peter_ym_account]

It looks like rendering the transparent objects before plain water, but after fancy water lets us get away with only rendering them once; the attached patch makes this change. Can anyone confirm whether the patch works, thanks.

[fcxSanya]

peter_ym_account you can add the "review" keyword (like I did it) when you want that someone to checked your patch. Usually Philip does it in the next few days.

[peter_ym_account]

removing review keyword for now -- it seems alpha blending over water with fancy water disabled is not quite right with this patch.

[peter_ym_account]

2nd try: changes transparent objects rendering behavior so they are rendered only once; except for the underwater portion when fancy water is disabled

[peter_ym_account]

I updated the patch - it now blends correctly in both fancy/plain water cases. Transparent objects are only rendered once, after the water, except when fancy water is disabled. When fancy water is disabled, a clipping plane is used to overdraw only the underwater portion (before the water).

As Philip mentioned, this means transparent objects everywhere will no longer look twice as opaque, which may require recalibrating art.

Critical feedback is appreciated! thanks

[Philip Taylor]

blending at edge of water

[Philip Taylor]

Thanks, seems mostly good - the clipping planes sound useful here.

I think this introduces a problem where fancy water uses alpha blending, mainly around the edges where it meets terrain. In the attachment there's some (white) terrain and a partially-submerged bush - the left screenshot is with this patch, the right screenshot is with the if (!m_WaterManager->WillRenderFancyWater()) line removed (so it renders twice). The left one cuts off too suddenly at the water, which isn't nice. (In deeper water it's okay because it's rendering the refraction texture instead of blending.)

With fancy water disabled, the patch seems to actually reduce performance slightly, since it's still rendering as many polygons as before but now it's got the clipping plane too. Since the goal is to improve performance, that seems important to fix. I guess what we could possibly do is:

• Model.h could add flags MODELFLAG_ABOVEWATER, MODELFLAG_BELOWWATER
• Something like CModel::ValidatePosition (not sure if that's a great place) could set one or two of those flags, depending on whether the bounding box intersects the water plane.
• CRenderer::RenderTransparentModels can pass a flag filter to Render.
• Then the pre-/post-water calls to RenderTransparentModels can tell it to filter out objects that aren't (at least partially) below/above the water. (Also the reflection and refraction code can then filter out objects on the wrong side of the water, so this seems useful for more than just transparent objects.)

[(none)]

Milestone Unclassified deleted

[peter_ym_account]

thanks for the feedback! I'll have to revisit the approach.

[Philip Taylor]

Reviewed already - I think we need to do something roughly like in my earlier comment.

(Moving to Alpha 5 since that might be a good time to sort out these graphics things.)

[Philip Taylor]

Replying to Philip:

Model.h could add flags MODELFLAG_ABOVEWATER, MODELFLAG_BELOWWATER. Something like CModel::ValidatePosition (not sure if that's a great place) could set one or two of those flags, depending on whether the bounding box intersects the water plane.

I don't think that's a good idea now - we ought to add a decent culling system so we can find all objects in the frustum below the water, render them, find all the ones above, render them, etc, instead of special-casing this with extra flags. (The culling system is probably mostly a separate task from this.)

[philip]

(In [9814]) Graphics optimisations and features from eihrul. Add shadow filtering (PCF) option. Fix ugly shadow saturation in old lighting mode. Fix fancy water shader. Fix camera matrix computation. Support scissoring of camera frustum. Optimise vertex skinning. Inline various matrix functions. Support filtering of the list of submitted models before a rendering pass, for more precise culling. Optimise water renderer (fixes #721, based on patch by ortalo). Use scissoring when generating reflection/refraction textures. Skip reflection/refraction texture generation when no water is visible. Render alpha-blended objects differently (fixes #434). Reduce shadow swimming effects.