float alphaModifier = 0.25;float4 main(...){ float4 texSample = ... texSample.rgb *= texSample.a * alphaModifier; return texSample;}Quote:Original post by Hodgman
RTT isn't that crazy... :)
If we assume a black background instead of a white background, it's possible. You could render your whole GUI onto this black background, and then composite the final result over your actual background.
In the case of your squares, we could say they've got 100% alpha, which is then modified to be 25% alpha.
The blend mode you'd want is:
Source * ModAlpha + Dest * (1-OrigAlpha)
where:
OrigAlpha = 100%
ModAlpha = 100% * 25%
However, that blend mode is too complicated to be configured though the built in blend unit, so you'd have to implement some of it in a shader.
You could use a shader to pre-multiply your alpha into the colour output, like:*** Source Snippet Removed ***And then use pre-multiplied-alpha blending:
Source * One + Dest * (1-SrcAlpha)
Quote:Original post by Krohm
Cannot you just disable Ztest and draw them? If the GUI elements are 2D, it will work just fine.
Quote:It seems as if the only way to do it properly is to draw to a rendertarget first, but that seems unnecessarily wasteful (and complicated, performance-wise).Using the blend mode above, you just need one RT for your entire GUI, which shouldn't be too complicated. On modern cards, performance isn't an issue for RTT, except for where you blend both RT's together (a small fraction of a ms).
Quote:Original post by HodgmanQuote:It seems as if the only way to do it properly is to draw to a rendertarget first, but that seems unnecessarily wasteful (and complicated, performance-wise).Using the blend mode above, you just need one RT for your entire GUI, which shouldn't be too complicated. On modern cards, performance isn't an issue for RTT, except for where you blend both RT's together (a small fraction of a ms).
If you want to save RAM, you could make this RT as big as your biggest GUI, and render each GUI into it (and blit to main screen) one at a time.
Quote:Original post by karwosts
Can you do regular alpha blending, but render from front to back with z testing?
I.e. draw the red square first with blending, and then render the green square second. It will reject everything underneath the red square, while drawing the green square around the red. This means each element only gets blended once with the background.
