Fix OpenGL sprite clipping

Port of upstream merge request !2650 with some improvements ported from blankart

Before

After

src/hardware/hw_main.c

@@ -3129,18 +3129,25 @@ static void HWR_SplitSprite(gl_vissprite_t *spr)
 		baseWallVerts[0].t = baseWallVerts[1].t = ((GLPatch_t *)gpatch->hardware)->max_t;
 	}
 
-	// if it has a dispoffset, push it a little towards the camera
-	if (spr->dispoffset) {
-		float co = -gl_viewcos*(0.05f*spr->dispoffset);
-		float si = -gl_viewsin*(0.05f*spr->dispoffset);
-		baseWallVerts[0].z = baseWallVerts[3].z = baseWallVerts[0].z+si;
-		baseWallVerts[1].z = baseWallVerts[2].z = baseWallVerts[1].z+si;
-		baseWallVerts[0].x = baseWallVerts[3].x = baseWallVerts[0].x+co;
-		baseWallVerts[1].x = baseWallVerts[2].x = baseWallVerts[1].x+co;
+
+
+	// push it toward the camera to mitigate floor-clipping sprites
+	if (!R_ThingIsPaperSprite(spr->mobj)) // but not for papersprites
+	{
+		// Let dispoffset work first since this adjust each vertex
+		HWR_RotateSpritePolyToAim(spr, baseWallVerts, false);
+
+		// push it toward the camera to mitigate floor-clipping sprites
+		float sprdist = sqrtf((spr->x1 - gl_viewx)*(spr->x1 - gl_viewx) + (spr->z1 - gl_viewy)*(spr->z1 - gl_viewy) + (spr->gzt - gl_viewz)*(spr->gzt - gl_viewz));
+		float distfact = ((2.0f*spr->dispoffset) + 20.0f) / sprdist;
+		for (i = 0; i < 4; i++)
+		{
+			baseWallVerts[i].x += (gl_viewx - baseWallVerts[i].x)*distfact;
+			baseWallVerts[i].z += (gl_viewy - baseWallVerts[i].z)*distfact;
+			baseWallVerts[i].y += (gl_viewz - baseWallVerts[i].y)*distfact;
+		}
 	}
 
-	// Let dispoffset work first since this adjust each vertex
-	HWR_RotateSpritePolyToAim(spr, baseWallVerts, false);
 
 	realtop = top = baseWallVerts[3].y;
 	realbot = bot = baseWallVerts[0].y;
@@ -3596,21 +3603,40 @@ static void HWR_DrawSprite(gl_vissprite_t *spr)
 		wallVerts[0].t = wallVerts[1].t = ((GLPatch_t *)gpatch->hardware)->max_t;
 	}
 
-	if (!splat)
-	{
-		// if it has a dispoffset, push it a little towards the camera
-		if (spr->dispoffset) {
-			float co = -gl_viewcos*(0.05f*spr->dispoffset);
-			float si = -gl_viewsin*(0.05f*spr->dispoffset);
-			wallVerts[0].z = wallVerts[3].z = wallVerts[0].z+si;
-			wallVerts[1].z = wallVerts[2].z = wallVerts[1].z+si;
-			wallVerts[0].x = wallVerts[3].x = wallVerts[0].x+co;
-			wallVerts[1].x = wallVerts[2].x = wallVerts[1].x+co;
-		}
+	float sprdist = 0.0f, distfact = 0.0f;
+	size_t i;
 
+	if (!splat && !R_ThingIsPaperSprite(spr->mobj))
+	{
 		// Let dispoffset work first since this adjust each vertex
 		HWR_RotateSpritePolyToAim(spr, wallVerts, false);
+
+		// push it toward the camera to mitigate floor-clipping sprites
+		sprdist = sqrtf((spr->x1 - gl_viewx)*(spr->x1 - gl_viewx) + (spr->z1 - gl_viewy)*(spr->z1 -gl_viewy)+ (spr->gzt - gl_viewz)*(spr->gzt - gl_viewz));
+		distfact = ((2.0f* spr->dispoffset) + 20.0f) / sprdist;
+		for (i = 0; i < 4; i++)
+		{
+			wallVerts[i].x += (gl_viewx - wallVerts[i].x)*distfact;
+			wallVerts[i].z += (gl_viewy - wallVerts[i].z)*distfact;
+			wallVerts[i].y += (gl_viewz - wallVerts[i].y)*distfact;
+		}
 	}
+	else if (R_ThingIsFloorSprite(spr->mobj))
+	{
+		sprdist = sqrtf((spr->x1 - gl_viewx)*(spr->x1 - gl_viewx) + (spr->z1 - gl_viewy)*(spr->z1 - gl_viewy));
+		distfact = (2.0f + 20.0f) / sprdist;
+
+		// pull splats out of the floor
+		for (i = 0; i < 4; i++)
+		{
+			wallVerts[i].x += (gl_viewx - wallVerts[i].x)*distfact;
+			wallVerts[i].z += (gl_viewy - wallVerts[i].z)*distfact;
+			wallVerts[i].y += (gl_viewz - wallVerts[i].y)*distfact;
+		}
+	}
+
+
+
 
 	// This needs to be AFTER the shadows so that the regular sprites aren't drawn completely black.
 	// sprite lighting by modulating the RGB components