[Causeless]

Summary

Two fixes for translucent drawing on the GPU renderer.

PrimitiveMan:DrawPrimitives(transValue, primitivesTable) drew nothing. The Transparency blend mode passed its blend amounts straight into the rteColor uniform. That included the alpha amount it ignores, which this overload always sets to 0. Every transparent primitive came out fully transparent, so stock callers like Decision Day's region boxes, the Scanner ping and the Automover controller's info box never showed. Transparency now draws at full colour with alpha = 1 − the average RGB amount, rounded to steps of 5 as before. The other blend modes are unchanged.

The other blend modes used their amounts backwards. Each amount went straight into the colour, so Screen, Multiply, Invert and the rest drew nothing at 0 and their full effect at 100. That is the reverse of the documented behaviour and of 6.2.2. The RGB amounts also scaled the colour, where 6.2.2 ignored them for these modes, and Screen ignored the alpha amount altogether. They now use only the alpha amount, as documented: 0 is the full effect and 100 is invisible, rounded to steps of 5. Invert and Dissolve take it as their alpha. The other blend equations take the colour premultiplied by it, which mixes the effect into the background by that much.

Translucent drawing came out darker than it should. Alpha blending lowers the backbuffer's alpha under anything translucent. Two copies of the frame then blended by that alpha onto a cleared buffer:

• the post-processing copy, which disables blending but was only drawn after blending was turned back on for the glows;
• in split-screen, the copy of each player screen into the backbuffer.

A half-transparent primitive came out 25% too dark, and darker still in split-screen. Both copies now draw without blending. Opaque pixels are unchanged, and translucent ones are a plain mix.

Testing

Screenshots from Decision Day in a muted test copy:

• First row is on development, the rocket primitive shows nothing
• Second row is after the drawing nothing was fixed
• Third row was after the translucent darkening was fixed