From 8871729a65615df0eab213bbbf942abe75771704 Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Sat, 8 Jul 2023 22:35:16 +0100
Subject: Avoid drawing the whole screen on each frame

This allows supporting 386DX "just about" (there will be flickering).
---
 src/vga.c | 59 ++++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 34 insertions(+), 25 deletions(-)

(limited to 'src/vga.c')

diff --git a/src/vga.c b/src/vga.c
index ec56b60..13013b2 100644
--- a/src/vga.c
+++ b/src/vga.c
@@ -10,16 +10,22 @@
 
 static uint8_t buffer[320 * 200];
 static uint8_t *screen = NULL;
+static uint8_t *target = NULL;
 
 uint8_t open_framebuffer()
 {
     if (__djgpp_nearptr_enable() == 0)
         return 0;
 
-    screen = (uint8_t *)(0xa0000 + __djgpp_conventional_base);
+    target = screen = (uint8_t *)(0xa0000 + __djgpp_conventional_base);
     return 1;
 }
 
+void blit_target(uint8_t t)
+{
+    target = t ? buffer : screen;
+}
+
 void close_framebuffer()
 {
     __djgpp_nearptr_disable();
@@ -91,94 +97,97 @@ void set_palette(const uint8_t *palette)
 
 void blit(const uint8_t *sprite, const Rect *dst)
 {
-    uint8_t *dbuffer = buffer + dst->x + dst->y * 320;
+    uint8_t b;
+    uint8_t *dtarget = target + dst->x + dst->y * 320;
 
     for (uint16_t j = dst->h; j > 0; j--)
     {
         for (uint16_t i = dst->w; i > 0; i--)
         {
-            uint8_t b = *sprite++;
+            b = *sprite++;
 
             /* transparent */
             if (b == TRANSPARENT)
             {
-                dbuffer++;
+                dtarget++;
                 continue;
             }
 
-            *dbuffer++ = b;
+            *dtarget++ = b;
         }
-        dbuffer += 320 - dst->w;
+        dtarget += 320 - dst->w;
     }
 }
 
 void blit_c(const uint8_t *sprite, const Rect *dst, uint8_t c)
 {
-    uint8_t *dbuffer = buffer + dst->x + dst->y * 320;
+    uint8_t b;
+    uint8_t *dtarget = target + dst->x + dst->y * 320;
 
     for (uint16_t j = dst->h; j > 0; j--)
     {
         for (uint16_t i = dst->w; i > 0; i--)
         {
-            uint8_t b = *sprite++;
+            b = *sprite++;
 
             /* transparent */
             if (b == TRANSPARENT)
             {
-                dbuffer++;
+                dtarget++;
                 continue;
             }
 
-            *dbuffer++ = b ? c : b;
+            *dtarget++ = b ? c : b;
         }
-        dbuffer += 320 - dst->w;
+        dtarget += 320 - dst->w;
     }
 }
 
 void blitrc(const uint8_t *sprite, const Rect *src, const Rect *dst)
 {
-    uint8_t *dbuffer = buffer + dst->x + dst->y * 320;
+    uint8_t b;
+    uint8_t *dtarget = target + dst->x + dst->y * 320;
     sprite += src->x + src->y * src->w;
 
     for (uint16_t j = dst->h; j > 0; j--)
     {
         for (uint16_t i = dst->w; i > 0; i--)
         {
-            uint8_t b = *sprite++;
+            b = *sprite++;
 
             /* transparent */
             if (b == TRANSPARENT)
             {
-                dbuffer++;
+                dtarget++;
                 continue;
             }
 
-            *dbuffer++ = b;
+            *dtarget++ = b;
         }
         sprite += src->w - dst->w;
-        dbuffer += 320 - dst->w;
+        dtarget += 320 - dst->w;
     }
 }
 
 void blit_erase(uint8_t c)
 {
-    memset(buffer, c, 320 * 200);
+    memset(target, c, 320 * 200);
 }
 
-void blit_update()
+void blit_copy_all()
 {
     memcpy(screen, buffer, 320 * 200);
 }
 
-void read_buffer(uint8_t *dst, const Rect *src)
+void blit_copy(const Rect *dst)
 {
-    uint8_t *s = buffer + src->y * 320 + src->x;
+    uint8_t *src = buffer + dst->x + dst->y * 320;
+    uint8_t *dtarget = screen + dst->x + dst->y * 320;
 
-    for (uint16_t j = src->h; j > 0; j--)
+    for (uint16_t j = dst->h; j > 0; j--)
     {
-        for (uint16_t i = src->w; i > 0; i--)
-            *dst++ = *s++;
-
-        s += 320 - src->w;
+        memcpy(dtarget, src, dst->w);
+        src += 320;
+        dtarget += 320;
     }
 }
-- 
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