From f8cc8a4bb316651f4f62d3380f1f57571d66c5a4 Mon Sep 17 00:00:00 2001
From: AliceLR <petrifiedrowan@gmail.com>
Date: Wed, 25 Oct 2023 15:56:20 -0600
Subject: [PATCH] Add renderer hook for DJGPP hardware SMZX mode.

---
 arch/djgpp/render_ega.c | 60 ++++++++++++++++++++++++-----------------
 src/graphics.c          | 11 ++++++++
 src/graphics.h          |  2 ++
 3 files changed, 49 insertions(+), 24 deletions(-)

diff --git a/arch/djgpp/render_ega.c b/arch/djgpp/render_ega.c
index 1531ff446..95e68f6f7 100644
--- a/arch/djgpp/render_ega.c
+++ b/arch/djgpp/render_ega.c
@@ -72,9 +72,10 @@ struct ega_render_data
   unsigned char flags;
   unsigned char oldmode;
   unsigned short vbsel;
+  unsigned char curpages;
+  boolean is_ati_card;
   uint8_t lines;
   uint8_t offset;
-  unsigned char curpages;
   uint32_t x;
   uint32_t y;
 };
@@ -94,7 +95,7 @@ static void ega_set_page(int page)
   __dpmi_int(0x10, &reg);
 }
 
-static void ega_set_smzx(void)
+static void ega_set_smzx(boolean is_ati)
 {
   // Super MegaZeux mode:
   // In a nutshell, this sets bit 6 of the VGA Mode Control Register.
@@ -107,6 +108,13 @@ static void ega_set_smzx(void)
   // and require a weird horizontal pixel shift value - see below.
   outportb(0x3C0, 0x10);
   outportb(0x3C0, 0x4C);
+
+  if(is_ati)
+  {
+    // set horizontal pixel shift to Undefined (0.5 pixels, in theory)
+    outportb(0x3C0, 0x13);
+    outportb(0x3C0, 0x01);
+  }
 }
 
 static void ega_set_16p(void)
@@ -218,6 +226,14 @@ static void ega_vsync(void)
     ;
 }
 
+static boolean ega_is_ati_card(void)
+{
+  // TODO: untested.
+  char ati_magic[9];
+  dosmemget(0xC0031, 9, ati_magic);
+  return memcmp("761295520", ati_magic, 9) == 0;
+}
+
 static boolean ega_init_video(struct graphics_data *graphics,
  struct config_info *conf)
 {
@@ -256,6 +272,8 @@ static boolean ega_init_video(struct graphics_data *graphics,
     render_data->flags = 0;
 
   render_data->oldmode = ega_get_mode();
+  render_data->is_ati_card = ega_is_ati_card();
+  render_data->smzx_swap_nibbles = render_data->is_ati_card;
 
   graphics->render_data = render_data;
   return set_video_mode();
@@ -272,23 +290,12 @@ static void ega_free_video(struct graphics_data *graphics)
   free(render_data);
 }
 
-static boolean ega_is_ati_card(void)
-{
-  // TODO: I don't know if this actually works!
-  char ati_magic[9];
-  dosmemget(0xC0031, 9, ati_magic);
-  return memcmp("761295520", ati_magic, 9) == 0;
-}
-
-static boolean ega_set_video_mode(struct graphics_data *graphics,
- int width, int height, int depth, boolean fullscreen, boolean resize)
+static boolean ega_set_screen_mode(struct graphics_data *graphics, unsigned mode)
 {
   struct ega_render_data *render_data = graphics->render_data;
   int i;
-  boolean ati_card = ega_is_ati_card();
 
   render_data->page = 0;
-  render_data->smzx_swap_nibbles = ati_card;
   render_data->lines = 255;
   render_data->offset = 255;
   render_data->x = 65535;
@@ -298,16 +305,8 @@ static boolean ega_set_video_mode(struct graphics_data *graphics,
     ega_set_14p();
 
   ega_set_mode(0x03);
-  if(graphics->screen_mode)
-  {
-    ega_set_smzx();
-    if(ati_card)
-    {
-      // set horizontal pixel shift to Undefined (0.5 pixels, in theory)
-      outportb(0x3C0, 0x13);
-      outportb(0x3C0, 0x01);
-    }
-  }
+  if(mode > 0)
+    ega_set_smzx(render_data->is_ati_card);
   ega_blink_off();
   ega_cursor_off();
 
@@ -326,6 +325,18 @@ static boolean ega_set_video_mode(struct graphics_data *graphics,
 
   render_data->flags |= TEXT_FLAGS_CHR;
 
+  // Unless someone makes a cursed VGA card specifically for MegaZeux,
+  // mode 3 does not exist in hardware and never has.
+  if(mode > 2)
+    return false;
+
+  return true;
+}
+
+static boolean ega_set_video_mode(struct graphics_data *graphics,
+ int width, int height, int depth, boolean fullscreen, boolean resize)
+{
+  ega_set_screen_mode(graphics, graphics->screen_mode);
   return true;
 }
 
@@ -497,6 +508,7 @@ void render_ega_register(struct renderer *renderer)
   renderer->init_video = ega_init_video;
   renderer->free_video = ega_free_video;
   renderer->set_video_mode = ega_set_video_mode;
+  renderer->set_screen_mode = ega_set_screen_mode;
   renderer->update_colors = ega_update_colors;
   renderer->resize_screen = resize_screen_standard;
   renderer->remap_char_range = ega_remap_char_range;
diff --git a/src/graphics.c b/src/graphics.c
index d05035b82..fd8722cc4 100644
--- a/src/graphics.c
+++ b/src/graphics.c
@@ -984,6 +984,7 @@ void set_screen_mode(unsigned int mode)
 
   fix_layer_screen_mode();
   graphics.palette_dirty = true;
+  graphics.smzx_dirty = true;
 }
 
 unsigned int get_screen_mode(void)
@@ -1112,6 +1113,16 @@ void update_screen(void)
     graphics.cursor_timestamp = ticks;
   }
 
+  if(graphics.smzx_dirty)
+  {
+    /* Request an SMZX mode change from the renderer, if applicable (EGA).
+     * Hardware SMZX may reset various text mode settings, so do it first.
+     */
+    graphics.smzx_dirty = false;
+    if(graphics.renderer.set_screen_mode)
+      graphics.renderer.set_screen_mode(&graphics, graphics.screen_mode);
+  }
+
   if(graphics.palette_dirty)
   {
     update_palette();
diff --git a/src/graphics.h b/src/graphics.h
index 3e67ecfc7..020af8266 100644
--- a/src/graphics.h
+++ b/src/graphics.h
@@ -120,6 +120,7 @@ struct renderer
   void    (*free_video)       (struct graphics_data *);
   boolean (*set_video_mode)   (struct graphics_data *, int width, int height,
                                 int depth, boolean fullscreen, boolean resize);
+  boolean (*set_screen_mode)  (struct graphics_data *, unsigned mode);
   void    (*update_colors)    (struct graphics_data *, struct rgb_color *palette,
                                 unsigned int count);
   void    (*resize_screen)    (struct graphics_data *, int width, int height);
@@ -178,6 +179,7 @@ struct graphics_data
   boolean renderer_is_headless;
   boolean default_smzx_loaded;
   boolean palette_dirty;
+  boolean smzx_dirty;
   boolean fade_status;
   boolean dialog_fade_status;
   boolean requires_extended;