Implement additive colour on walls and sprites

Also, don't modify the alpha channel when adding the additive colour.

src/hwrenderer/scene/hw_sprites.cpp

@@ -159,6 +159,7 @@ void GLSprite::DrawSprite(HWDrawInfo *di, FRenderState &state, bool translucent)
 				: ThingColor.Modulate(cursec->SpecialColors[sector_t::sprites]);
 
 			state.SetObjectColor(finalcol);
+			state.SetAddColor(cursec->SpecialColors[sector_t::add]);
 		}
 		state.SetColor(lightlevel, rel, di->isFullbrightScene(), Colormap, trans);
 	}
@@ -295,6 +296,7 @@ void GLSprite::DrawSprite(HWDrawInfo *di, FRenderState &state, bool translucent)
 	}
 
 	state.SetObjectColor(0xffffffff);
+	state.SetAddColor(0);
 	state.EnableTexture(true);
 	state.SetDynLight(0, 0, 0);
 }

src/hwrenderer/scene/hw_walls.cpp

@@ -174,6 +174,7 @@ void GLWall::RenderTexturedWall(HWDrawInfo *di, FRenderState &state, int rflags)
 		PalEntry color2 = side->GetSpecialColor(tierndx, side_t::wallbottom, frontsector);
 		state.SetObjectColor(color1);
 		state.SetObjectColor2(color2);
+		state.SetAddColor(seg->frontsector->SpecialColors[sector_t::add]);
 		if (color1 != color2)
 		{
 			// Do gradient setup only if there actually is a gradient.
@@ -238,6 +239,7 @@ void GLWall::RenderTexturedWall(HWDrawInfo *di, FRenderState &state, int rflags)
 	}
 	state.SetObjectColor(0xffffffff);
 	state.SetObjectColor2(0);
+	state.SetAddColor(0);
 	state.SetTextureMode(tmode);
 	state.EnableGlow(false);
 	state.EnableGradient(false);

src/hwrenderer/scene/hw_weapon.cpp

@@ -72,6 +72,7 @@ void HWDrawInfo::DrawPSprite(HUDSprite *huds, FRenderState &state)
 	state.SetRenderStyle(huds->RenderStyle);
 	state.SetTextureMode(huds->RenderStyle);
 	state.SetObjectColor(huds->ObjectColor);
+	// state.SetAddColor(0);
 	state.SetDynLight(huds->dynrgb[0], huds->dynrgb[1], huds->dynrgb[2]);
 	state.EnableBrightmap(!(huds->RenderStyle.Flags & STYLEF_ColorIsFixed));
 
@@ -94,6 +95,7 @@ void HWDrawInfo::DrawPSprite(HUDSprite *huds, FRenderState &state)
 	state.SetTextureMode(TM_NORMAL);
 	state.AlphaFunc(Alpha_GEqual, gl_mask_sprite_threshold);
 	state.SetObjectColor(0xffffffff);
+	state.SetAddColor(0);
 	state.SetDynLight(0, 0, 0);
 	state.EnableBrightmap(false);
 }

wadsrc/static/shaders/glsl/main.fp

@@ -114,7 +114,7 @@ vec4 getTexel(vec2 st)
 	if (uObjectColor2.a == 0.0) texel *= uObjectColor;
 	else texel *= mix(uObjectColor, uObjectColor2, gradientdist.z);
 
-	texel += uAddColor;
+	texel.rgb += uAddColor.rgb;
 
 	return desaturate(texel);
 }