From bc0b5505a84596d6f4a437042dc57efda5c5957d Mon Sep 17 00:00:00 2001
From: Sryder13 <sryder13@gmail.com>
Date: Mon, 8 Sep 2014 00:55:32 +0100
Subject: [PATCH] OpenGL: Fix sky drawing

sky positioning and scaling more correct compared to software.
---
 src/hardware/hw_main.c | 59 ++++++++++++++++++++++++++----------------
 1 file changed, 36 insertions(+), 23 deletions(-)

diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index e832457c0..77c56a734 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -4355,7 +4355,7 @@ static void HWR_DrawSkyBackground(player_t *player)
 {
 	FOutVector v[4];
 	angle_t angle;
-	float f;
+	float dimensionmultiply;
 
 //  3--2
 //  | /|
@@ -4377,36 +4377,49 @@ static void HWR_DrawSkyBackground(player_t *player)
 
 	// X
 
-	if (textures[skytexture]->width > 256)
-		angle = (angle_t)((float)(dup_viewangle + gr_xtoviewangle[0])
-						/((float)textures[skytexture]->width/256.0f))
-							%(ANGLE_90-1);
-	else
-		angle = (dup_viewangle + gr_xtoviewangle[0])%(ANGLE_90-1);
+	// NOTE: This doesn't work right with texture widths greater than 1024
+	// software doesn't draw any further than 1024 for skies anyway, but this doesn't overlap properly
+	// The only time this will probably be an issue is when a sky wider than 1024 is used as a sky AND a regular wall texture
 
-	f = (float)((textures[skytexture]->width/2)
-	            * FIXED_TO_FLOAT(FINETANGENT((2048
-	 - ((INT32)angle>>(ANGLETOFINESHIFT + 1))) & FINEMASK)));
+	angle = (dup_viewangle + gr_xtoviewangle[0]);
 
-	v[0].sow = v[3].sow = 0.22f+(f)/(textures[skytexture]->width/2);
-	v[2].sow = v[1].sow = 0.22f+(f+(127))/(textures[skytexture]->width/2);
+	dimensionmultiply = ((float)textures[skytexture]->width/256.0f);
 
+	v[0].sow = v[3].sow = ((float) angle / ((ANGLE_90-1)*dimensionmultiply));
+	v[2].sow = v[1].sow = (-1.0f/dimensionmultiply)+((float) angle / ((ANGLE_90-1)*dimensionmultiply));
 
 	// Y
+	angle = aimingangle;
+	
+	float aspectratio = (float)vid.width/(float)vid.height;
+	dimensionmultiply = ((float)textures[skytexture]->height/(128.0f*aspectratio));
+	float angleturn = (((float)ANGLE_45-1.0f)*aspectratio)*dimensionmultiply;
 
-	if (textures[skytexture]->height > 256)
-		angle = (angle_t)((float)(aimingangle)
-						*(256.0f/(float)textures[skytexture]->height))
-							%(ANGLE_90-1); // Just so that looking up and down scales right
+	// Middle of the sky should always be at angle 0
+	// need to keep correct aspect ratio with X
+	if (atransform.flip)
+	{
+		// During vertical flip the sky should be flipped and it's y movement should also be flipped obviously
+		v[3].tow = v[2].tow = -(0.5f-(0.5f/dimensionmultiply));
+		v[0].tow = v[1].tow = (-1.0f/dimensionmultiply)-(0.5f-(0.5f/dimensionmultiply));
+	}
 	else
-		angle = (aimingangle);
+	{
+		v[3].tow = v[2].tow = (-1.0f/dimensionmultiply)-(0.5f-(0.5f/dimensionmultiply));
+		v[0].tow = v[1].tow = -(0.5f-(0.5f/dimensionmultiply));
+	}
 
-	f = (float)((textures[skytexture]->height/2)
-	            * FIXED_TO_FLOAT(FINETANGENT((2048
-	 - ((INT32)angle>>(ANGLETOFINESHIFT + 1))) & FINEMASK)));
-
-	v[3].tow = v[2].tow = 0.22f+(f)/(textures[skytexture]->height/2);
-	v[0].tow = v[1].tow = 0.22f+(f+(127))/(textures[skytexture]->height/2);
+	if (angle > ANGLE_180) // Do this because we don't want the sky to suddenly teleport when crossing over 0 to 360 and vice versa
+	{
+		angle = InvAngle(angle);
+		v[3].tow = v[2].tow += ((float) angle / angleturn);
+		v[0].tow = v[1].tow += ((float) angle / angleturn);
+	}
+	else
+	{
+		v[3].tow = v[2].tow -= ((float) angle / angleturn);
+		v[0].tow = v[1].tow -= ((float) angle / angleturn);
+	}
 
 	HWD.pfnDrawPolygon(NULL, v, 4, 0);
 }