From 1c1e91bd8bf4e9d08cd4d8ee41568e3d25ee8256 Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Tue, 6 Jun 2023 22:58:48 +0100
Subject: First stab at the sw blitter

---
 data/sprites.png | Bin 345 -> 9174 bytes
 src/main.c       |  45 +++++++++++++++++++++++++++++++++++----------
 src/vga.c        |  42 +++++++++++++++++++++++++++++++++++++++---
 src/vga.h        |   9 ++++++++-
 4 files changed, 82 insertions(+), 14 deletions(-)

diff --git a/data/sprites.png b/data/sprites.png
index bfe73d4..6ca0043 100644
Binary files a/data/sprites.png and b/data/sprites.png differ
diff --git a/src/main.c b/src/main.c
index 9876404..89ae860 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,7 +1,7 @@
 #include <stdint.h>
-#include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <crt0.h>
 
 #include "keyb.h"
@@ -29,25 +29,50 @@ int main(int argc, char *argv[])
 
     set_palette(binary_palette_start);
 
-    uint8_t *screen = open_framebuffer();
-    if (!screen)
+    if (!open_framebuffer())
     {
         set_mode(3);
         fprintf(stderr, "ERROR: failed to open the framebuffer\n");
         return 1;
     }
 
-    int i = 0;
+    blit_erase(0);
+
+    uint8_t bg[24 * 24] = { 0 };
+    uint16_t x = 10, y = 10;
+    int8_t ix = 1, iy = 1;
+    uint8_t c = 0;
+
     while (!keys[KEY_ESC])
     {
-        wait_vsync();
+        // erase
+        blit(bg, x, y, 24, 24);
 
-        memset(screen, i, 320 * 200);
-        i++;
-        if (i > 15)
-            i = 0;
+        x += ix;
+        y += iy;
+
+        if (x >= 320 - 24 || x == 0)
+        {
+            ix *= -1;
+            c = (c + 1) % 15;
+            blit_erase(c);
+            memset(bg, c, 24 * 24);
+        }
+        if (y >= 200 - 24 || y == 0)
+        {
+            iy *= -1;
+            c = (c + 1) % 15;
+            blit_erase(c);
+            memset(bg, c, 24 * 24);
+        }
+
+        // draw
+        blit(binary_sprites_start, x, y, 24, 24);
+
+        wait_vsync();
+        blit_update();
 
-        timer_wait(1);
+        //timer_wait(1);
     }
 
     set_mode(3);
diff --git a/src/vga.c b/src/vga.c
index 981ad6f..e2fb7f9 100644
--- a/src/vga.c
+++ b/src/vga.c
@@ -1,15 +1,22 @@
 #include <stdlib.h>
+#include <string.h>
 #include <stdint.h>
 #include <dpmi.h>
 #include <sys/nearptr.h>
 #include <pc.h>
 
-uint8_t *open_framebuffer()
+#include "vga.h"
+
+static uint8_t buffer[320 * 200];
+static uint8_t *screen = NULL;
+
+uint8_t open_framebuffer()
 {
     if (__djgpp_nearptr_enable() == 0)
-        return NULL;
+        return 0;
 
-    return (uint8_t *)(0xa0000 + __djgpp_conventional_base);
+    screen = (uint8_t *)(0xa0000 + __djgpp_conventional_base);
+    return 1;
 }
 
 void close_framebuffer()
@@ -36,3 +43,32 @@ void set_palette(const uint8_t *palette)
     for (int i = 0; i < 768; i++)
         outportb(0x3c9, palette[i] >> 2);
 }
+
+void blit(const uint8_t *src, uint16_t x, uint16_t y, uint16_t w, uint16_t h)
+{
+    for (int32_t j = y; j < y + h; j++)
+        for (int32_t i = x; i < x + w; i++)
+        {
+            uint8_t b = *src++;
+
+            /* transparent */
+            if (b == TRANSPARENT)
+                continue;
+
+            /* clipping */
+            if (i < 0 || i >= 320 || j < 0 || j >= 200)
+                continue;
+
+            buffer[i + j * 320] = b;
+        }
+}
+
+void blit_erase(uint8_t c)
+{
+    memset(buffer, c, 320 * 200);
+}
+
+void blit_update()
+{
+    memcpy(screen, buffer, 320 * 200);
+}
diff --git a/src/vga.h b/src/vga.h
index be90b29..ef183ca 100644
--- a/src/vga.h
+++ b/src/vga.h
@@ -1,7 +1,10 @@
 #ifndef _VGA_H
 #define _VGA_H
 
-uint8_t *open_framebuffer();
+/* palette index to be used as transparent color */
+#define TRANSPARENT 16
+
+uint8_t open_framebuffer();
 void close_framebuffer();
 
 void set_mode(uint8_t mode);
@@ -10,4 +13,8 @@ void wait_vsync();
 /* the palette is expected to be 8 bit per color, and will be converted to VGA's 6 bit per color */
 void set_palette(const uint8_t *palette);
 
+void blit(const uint8_t *src, uint16_t x, uint16_t y, uint16_t w, uint16_t h);
+void blit_erase(uint8_t c);
+void blit_update();
+
 #endif /* _VGA_H */
-- 
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