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Significant transparency difference on different GPU's

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K24A3:
I'm using low transparency on my three multilayered skyboxes (3DS files not the jPCT skybox) and have found that there is a huge difference on two different GPU's, namely the Tegra2 and PowerVR (Omap 4430).

To equalize the transparency on both devices, I need to set the transparency much higher on the PowerVR.

Using Transparency of 4 looks vibrant on the Tegra2, but almost black on the PowerVR.
Using Transparency of 16 looks great on the PowerVR but too bright and very washed out on the Tegra2.

Setting the transparency to Additive doesn't resolve the problem.
I tried setting the transparency of the layers incrementally (for example 2, then 4, then 8 ) but that doesn't help.

I'm assuming it's a design trait of the GPU's in question, so the solution would be to detect the GPU and set the transparency accordingly or let the user modify the values manually.

Is this a generally known issue? Does jPCT calculate transparency based on OpenGL flags? Or am I missing something?

(OpenGL ES 1.1, jPCT 1.24)

EgonOlsen:
No, jPCT just sets the requested value via OpenGL. What the GPU do what that value is up to them. It could also be related to the used color depth...maybe that's different!?
Anyway, i can't anything about it....i think. To be 100% sure, some screen shots would help.

K24A3:
This is interesting, I took screenshots on both devices and they look almost identical in the images. So it must be a result of the manufactures screen calibration or something. I'll add an option to let the user change it manually.

Thanks.

(Edit: Color depth is 32bit on both devices)

K24A3:
I've ran into a strange transparency glitch that I can't figure out.

I have a transparent skybox/sphere using additive transparency, with normal transparent 3D objects inside.
Intermittently the brightness of the objects change drastically. For 20 seconds they look normal, then suddenly drop in brightness for no apparent reason as if a light went out.

I have disabled all lights except for ambient but it still happens.
If I make the skybox solid (no transparency) the problem goes away.
If I make the objects solid the problem goes away.

So I'm thinking it's a transparency calculation problem in either OpenGL or jPCT since it's happening on two totally different GPU's.

Have you seen this kind of behavior before?
I'm currently putting together a test app to send to you.

EgonOlsen:

--- Quote from: K24A3 on January 23, 2012, 01:06:42 pm ---Have you seen this kind of behavior before?
I'm currently putting together a test app to send to you.

--- End quote ---
Yes, i've seem something like this lately, but in the desktop version. I'm not sure right now, if this was something to fix in jPCT-AE as well and if it was, if i actually did it. I'll wait for your test case and check it out...

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