From dc0e6d40a48facd1743606b279db30e5ec002c21 Mon Sep 17 00:00:00 2001
From: Magnus Norddahl <dpjudas@users.noreply.github.com>
Date: Wed, 9 Nov 2016 11:38:07 +0100
Subject: [PATCH] Distance sort sprites

---
 src/r_poly.cpp | 28 +++++++++++++++++++++++++++-
 src/r_poly.h   | 24 ++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/src/r_poly.cpp b/src/r_poly.cpp
index a823d94f7..978e0a1f4 100644
--- a/src/r_poly.cpp
+++ b/src/r_poly.cpp
@@ -47,6 +47,10 @@ void RenderPolyBsp::Render()
 	SolidSegments.push_back({ -0x7fff, 0 });
 	SolidSegments.push_back({ viewwidth, 0x7fff });
 
+	SectorSpriteRanges.clear();
+	SectorSpriteRanges.resize(numsectors);
+	SortedSprites.clear();
+
 	// Perspective correct:
 	float ratio = WidescreenRatio;
 	float fovratio = (WidescreenRatio >= 1.3f) ? 1.333333f : ratio;
@@ -174,8 +178,10 @@ void RenderPolyBsp::RenderSubsector(subsector_t *sub)
 		PolyTriangleDrawer::draw(uniforms, vertices, sub->numlines, TriangleDrawMode::Fan, true, 0, viewwidth, 0, viewheight, ceiltex);
 	}
 
-	for (AActor *thing = sub->sector->thinglist; thing != nullptr; thing = thing->snext)
+	SpriteRange sprites = GetSpritesForSector(sub->sector);
+	for (int i = 0; i < sprites.Count; i++)
 	{
+		AActor *thing = SortedSprites[sprites.Start + i].Thing;
 		if ((thing->renderflags & RF_SPRITETYPEMASK) == RF_WALLSPRITE)
 			AddWallSprite(thing, sub);
 		else
@@ -183,6 +189,26 @@ void RenderPolyBsp::RenderSubsector(subsector_t *sub)
 	}
 }
 
+SpriteRange RenderPolyBsp::GetSpritesForSector(sector_t *sector)
+{
+	if (SectorSpriteRanges.size() < sector->sectornum || sector->sectornum < 0)
+		return SpriteRange();
+
+	auto &range = SectorSpriteRanges[sector->sectornum];
+	if (range.Start == -1)
+	{
+		range.Start = (int)SortedSprites.size();
+		range.Count = 0;
+		for (AActor *thing = sector->thinglist; thing != nullptr; thing = thing->snext)
+		{
+			SortedSprites.push_back({ thing, (thing->Pos() - ViewPos).LengthSquared() });
+			range.Count++;
+		}
+		std::stable_sort(SortedSprites.begin() + range.Start, SortedSprites.begin() + range.Start + range.Count);
+	}
+	return range;
+}
+
 void RenderPolyBsp::AddLine(seg_t *line, sector_t *frontsector)
 {
 	// Reject lines not facing viewer
diff --git a/src/r_poly.h b/src/r_poly.h
index 6248e02f7..7e26f8ce6 100644
--- a/src/r_poly.h
+++ b/src/r_poly.h
@@ -49,6 +49,26 @@ public:
 	FDynamicColormap *Colormap = nullptr;
 };
 
+// Used for sorting things by distance to the camera
+class PolySortedSprite
+{
+public:
+	PolySortedSprite(AActor *thing, double distanceSquared) : Thing(thing), DistanceSquared(distanceSquared) { }
+	bool operator<(const PolySortedSprite &other) const { return DistanceSquared > other.DistanceSquared; }
+
+	AActor *Thing;
+	double DistanceSquared;
+};
+
+class SpriteRange
+{
+public:
+	SpriteRange() = default;
+	SpriteRange(int start, int count) : Start(start), Count(count) { }
+	int Start = -1;
+	int Count = 0;
+};
+
 // Renders a GL BSP tree in a scene
 class RenderPolyBsp
 {
@@ -67,6 +87,7 @@ private:
 	bool IsThingCulled(AActor *thing);
 	visstyle_t GetSpriteVisStyle(AActor *thing, double z);
 	FTexture *GetSpriteTexture(AActor *thing, /*out*/ bool &flipX);
+	SpriteRange GetSpritesForSector(sector_t *sector);
 
 	void RenderPlayerSprites();
 	void RenderPlayerSprite(DPSprite *sprite, AActor *owner, float bobx, float boby, double wx, double wy, double ticfrac);
@@ -85,6 +106,9 @@ private:
 	std::vector<subsector_t *> PvsSectors;
 	TriMatrix worldToClip;
 
+	std::vector<SpriteRange> SectorSpriteRanges;
+	std::vector<PolySortedSprite> SortedSprites;
+
 	std::vector<PolyScreenSprite> ScreenSprites;
 
 	const int BaseXCenter = 160;