From adff38b97862d678ee37574e1a89e5fbdaef5d8a Mon Sep 17 00:00:00 2001
From: Nico de Poel <ndepoel@gmail.com>
Date: Sat, 14 Jan 2023 14:32:58 +0100
Subject: [PATCH] Expanded display initialization code with proper handling of
 both NTSC and PAL aspect ratios, and allowing PAL to render at higher
 resolution. Also includes provisioning for switching between progressive and
 interlaced modes.

---
 display.c | 56 ++++++++++++++++++++++++++++++++++++++++++-------------
 display.h |  6 ++++--
 2 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/display.c b/display.c
index 86c057f..9cc0a6b 100644
--- a/display.c
+++ b/display.c
@@ -47,7 +47,7 @@ MATRIX vp_matrix;
 u_long *curOT;
 
 // Scale X coordinates to correct the aspect ratio for the chosen resolution
-VECTOR aspect_scale = { SCREENWIDTH * ONE / 320 , ONE, ONE };
+VECTOR aspect_scale = { SCREENWIDTH * ONE / 320, ONE, ONE };
 
 void display_init()
 {
@@ -55,15 +55,9 @@ void display_init()
 	// ISR subsystem to the kernel
 	ResetGraph(0);
 
-	//SetVideoMode(MODE_NTSC);
-	
-	// Define display environments, first on top and second on bottom
-	SetDefDispEnv(&disp[0], 0, 0, SCREENWIDTH, SCREENHEIGHT);
-	SetDefDispEnv(&disp[1], 0, SCREENHEIGHT, SCREENWIDTH, SCREENHEIGHT);
-	
-	// Define drawing environments, first on bottom and second on top
-	SetDefDrawEnv(&draw[0], 0, SCREENHEIGHT, SCREENWIDTH, SCREENHEIGHT);
-	SetDefDrawEnv(&draw[1], 0, 0, SCREENWIDTH, SCREENHEIGHT);
+	// Start the display in progressive mode
+	int screenHeight;
+	display_reset(0, &screenHeight);
 	
 	// Set and enable clear color
 	setRGB0(&draw[0], 49, 77, 121);
@@ -84,14 +78,51 @@ void display_init()
 	FntLoad(960, 0);
 	
 	// Open up a test font text stream
-	FntOpen(0, 8, SCREENWIDTH, SCREENHEIGHT, 0, 512);
+	FntOpen(0, 8, SCREENWIDTH, screenHeight, 0, 512);
 
     // Initialize GTE
     InitGeom();
-	gte_SetGeomOffset(SCREENWIDTH >> 1, SCREENHEIGHT >> 1);
+	gte_SetGeomOffset(SCREENWIDTH >> 1, screenHeight >> 1);
 	gte_SetGeomScreen(180);	// Screen depth for FOV control. Determines the distance of the camera to the near plane.
 }
 
+void display_reset(u_char interlaced, int *outScreenHeight)
+{
+	int screenHeight, yOffset;
+	if (GetVideoMode() == MODE_NTSC)
+	{
+		screenHeight = SCREENHEIGHT_NTSC;
+		yOffset = (240 - SCREENHEIGHT_NTSC) >> 1;	// Vertically center the image for NTSC displays
+
+		// Scale Y coordinates to correct the aspect ratio for NTSC's typical visible screen area
+		aspect_scale.vy = 224 * ONE / 240;
+	}
+	else	// MODE_PAL
+	{
+		screenHeight = SCREENHEIGHT_PAL;
+		yOffset = (288 - SCREENHEIGHT_PAL) >> 1;	// Vertically center the image for PAL displays
+
+		// Scale Y coordinates to correct the aspect ratio for PAL's non-square pixels
+		aspect_scale.vy = 256 * ONE / 240;
+	}
+
+	// Define display environments, first on top and second on bottom
+	SetDefDispEnv(&disp[0], 0, 0, SCREENWIDTH, screenHeight);
+	SetDefDispEnv(&disp[1], 0, screenHeight, SCREENWIDTH, screenHeight);
+
+	// Define drawing environments, first on bottom and second on top
+	SetDefDrawEnv(&draw[0], 0, screenHeight, SCREENWIDTH, screenHeight);
+	SetDefDrawEnv(&draw[1], 0, 0, SCREENWIDTH, screenHeight);
+
+	disp[0].screen.y = disp[1].screen.y = yOffset;
+	disp[0].screen.h = disp[1].screen.h = screenHeight;
+
+	gte_SetGeomOffset(SCREENWIDTH >> 1, screenHeight >> 1);
+
+	if (outScreenHeight != NULL)
+		*outScreenHeight = screenHeight;
+}
+
 void display_start()
 {
     curOT = ot[db];
@@ -143,7 +174,6 @@ void *display_allocPrim(size_t size)
     if (nextpri + size > primbuff[db] + PRIMBUFLEN)
         return NULL;
 
-    // TODO: maybe add a bounds check?
     void *prim = nextpri;
     nextpri += size;
     return prim;
diff --git a/display.h b/display.h
index 5b88d96..fd4ded0 100644
--- a/display.h
+++ b/display.h
@@ -1,8 +1,9 @@
 #ifndef __DISPLAY_H__
 #define __DISPLAY_H__
 
-#define SCREENWIDTH		512
-#define SCREENHEIGHT	240
+#define SCREENWIDTH		    512
+#define SCREENHEIGHT_NTSC   240
+#define SCREENHEIGHT_PAL    256
 
 #define OTLEN	1024
 
@@ -10,6 +11,7 @@ extern MATRIX vp_matrix;
 extern u_long *curOT;
 
 void display_init();
+void display_reset(u_char interlaced, int *outScreenHeight);
 void display_start();
 void display_finish();