renderer: implement high precision rendering framebuffers

This is needed to avoid color-banding with the various
division/multiplication round trips of the complete overBright
implementation. This will also be needed for sRGB colors in the
future too. It is enabled by default if a feature requires it.

This is optional and can be disabled with r_highPrecisionRendering,
or automatically disabled if the hardware doesn't support the feature.

Author: illwieckz

src/engine/renderer/tr_image.cpp

@@ -2408,13 +2408,24 @@ static void R_CreateCurrentRenderImage()
 
 	imageParams_t imageParams = {};
 	imageParams.bits = IF_NOPICMIP;
+
+	bool bestWithHighPrecisionFrameBuffer = !r_mapClampOverBright.Get();
+
+	if ( bestWithHighPrecisionFrameBuffer && glConfig2.textureFloatAvailable && r_highPrecisionRendering.Get() )
+	{
+		imageParams.bits |= IF_RGBA16;
+	}
+
 	imageParams.filterType = filterType_t::FT_NEAREST;
 	imageParams.wrapType = wrapTypeEnum_t::WT_CLAMP;
 
 	tr.currentRenderImage[0] = R_CreateImage( "_currentRender[0]", nullptr, width, height, 1, imageParams );
 	tr.currentRenderImage[1] = R_CreateImage( "_currentRender[1]", nullptr, width, height, 1, imageParams );
 
-	imageParams.bits |= IF_PACKED_DEPTH24_STENCIL8;
+	imageParams = {};
+	imageParams.bits = IF_NOPICMIP | IF_PACKED_DEPTH24_STENCIL8;
+	imageParams.filterType = filterType_t::FT_NEAREST;
+	imageParams.wrapType = wrapTypeEnum_t::WT_CLAMP;
 
 	tr.currentDepthImage = R_CreateImage( "_currentDepth", nullptr, width, height, 1, imageParams );
 }

src/engine/renderer/tr_init.cpp

@@ -186,6 +186,9 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 	cvar_t      *r_halfLambertLighting;
 	cvar_t      *r_rimLighting;
 	cvar_t      *r_rimExponent;
+
+	Cvar::Cvar<bool> r_highPrecisionRendering("r_highPrecisionRendering", "use high precision frame buffers for rendering and blending", Cvar::NONE, true);
+
 	cvar_t      *r_gamma;
 	cvar_t      *r_lockpvs;
 	cvar_t      *r_noportals;
@@ -1254,6 +1257,8 @@ ScreenshotCmd screenshotPNGRegistration("screenshotPNG", ssFormat_t::SSF_PNG, "p
 		r_rimExponent = Cvar_Get( "r_rimExponent", "3", CVAR_CHEAT | CVAR_LATCH );
 		AssertCvarRange( r_rimExponent, 0.5, 8.0, false );
 
+		Cvar::Latch( r_highPrecisionRendering );
+
 		r_drawBuffer = Cvar_Get( "r_drawBuffer", "GL_BACK", CVAR_CHEAT );
 		r_lockpvs = Cvar_Get( "r_lockpvs", "0", CVAR_CHEAT );
 		r_noportals = Cvar_Get( "r_noportals", "0", CVAR_CHEAT );

src/engine/renderer/tr_local.h

@@ -3030,6 +3030,8 @@ enum class dynamicLightRenderer_t { LEGACY, TILED };
 	extern cvar_t *r_rimLighting;
 	extern cvar_t *r_rimExponent;
 
+	extern Cvar::Cvar<bool> r_highPrecisionRendering;
+
 	extern cvar_t *r_logFile; // number of frames to emit GL logs
 
 	extern cvar_t *r_clear; // force screen clear every frame