Add dirty lines and redraw optimization to ppu

2 files changed, 42 insertions, 10 deletions

diff --git a/src/main.c b/src/main.c
index fc073c9..e2b39b8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -44,6 +44,10 @@ docolors(Device *d) {
     for(size_t i = 4; i < 16; ++i) {
         palette[i] = palette[i / 4];
     }
+
+    // Redraw the screen if we change the color palette.
+    reqdraw = 1;
+    redraw_screen();
 }
 
 void
@@ -74,6 +78,7 @@ screen_talk(Device *d, u8 b0, u8 w) {
         Uint16 y = mempeek16(d->dat, 0xa);
         Uint8 layer = d->dat[0xe] >> 4 & 0x1;
         ppu_pixel(&ppu, layer, x, y, d->dat[0xe] & 0x3);
+        reqdraw = 1;
     } else if(w && b0 == 0xf) {
         Uint16 x = mempeek16(d->dat, 0x8);
         Uint16 y = mempeek16(d->dat, 0xa);
@@ -83,6 +88,7 @@ screen_talk(Device *d, u8 b0, u8 w) {
             ppu_2bpp(&ppu, layer, x, y, addr, d->dat[0xf] & 0xf, d->dat[0xf] >> 0x4 & 0x1, d->dat[0xf] >> 0x5 & 0x1);
         else
             ppu_1bpp(&ppu, layer, x, y, addr, d->dat[0xf] & 0xf, d->dat[0xf] >> 0x4 & 0x1, d->dat[0xf] >> 0x5 & 0x1);
+        reqdraw = 1;
     }
 }
 
@@ -153,10 +159,6 @@ void main(void) {
         uxn_eval(&u, mempeek16(devscreen->dat, 0));
 
         // Blit ppu.pixels to the framebuffer.
-        // NOTE: This is very inefficient, we likely want to keep track of the
-        // lines/tiles that have changed and only copy those.
-        for (size_t i = 0; i < SCREEN_WIDTH * SCREEN_HEIGHT; i++) {
-            framebuffer[i] = palette[ppu.pixels[i]];
-        }
+        blit_framebuffer(&ppu);
     }
 }
diff --git a/src/ppu.c b/src/ppu.c
index aeb3699..85245b2 100644
--- a/src/ppu.c
+++ b/src/ppu.c
@@ -15,13 +15,15 @@ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 WITH REGARD TO THIS SOFTWARE.
 */
 
-#define SCREEN_WIDTH  64 * 8 / 2
-#define SCREEN_HEIGHT 40 * 8 / 2
+#define SCREEN_WIDTH  64 * 8
+#define SCREEN_HEIGHT 40 * 8
 
 static u32 *framebuffer = 0;
 
-static u32 palette[16];
-static u8 pixels_buf[SCREEN_WIDTH * SCREEN_HEIGHT];
+static u32 palette[16] = {0};
+static u8 pixels_buf[SCREEN_WIDTH * SCREEN_HEIGHT] = {0};
+static u8 dirty_lines[SCREEN_HEIGHT] = {0};
+static u8 reqdraw = 0;
 
 static Uint8 blending[5][16] = {
     {0, 0, 0, 0, 1, 0, 1, 1, 2, 2, 0, 2, 3, 3, 3, 0},
@@ -37,8 +39,8 @@ ppu_pixel(Ppu *p, Uint8 layer, Uint16 x, Uint16 y, Uint8 color)
     Uint8 *pixel = &p->pixels[idx], shift = layer * 2;
     if(x < p->width && y < p->height) {
         *pixel = (*pixel & ~(0x3 << shift)) | (color << shift);
-        // framebuffer[idx] = palette[*pixel];
     }
+    dirty_lines[y] |= 1;
 }
 
 void
@@ -75,6 +77,13 @@ ppu_2bpp(Ppu *p, Uint8 layer, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Ui
         }
 }
 
+void
+redraw_screen(void) {
+    for (size_t j = 0; j < SCREEN_HEIGHT; j++) {
+        dirty_lines[j] |= 1;
+    }
+}
+
 int
 ppu_init(Ppu *p, Uint8 hor, Uint8 ver) {
     p->width = 8 * hor;
@@ -135,5 +144,26 @@ ppu_init(Ppu *p, Uint8 hor, Uint8 ver) {
     palette[2] = 0x007777ff;
     palette[3] = 0x00ff7777;
 
+    // Make sure we perform an initial screen drawing.
+    reqdraw = 1;
+    redraw_screen();
+
     return 1;
 }
+
+void
+blit_framebuffer(Ppu *p) {
+    if (reqdraw == 0) {
+        return;
+    }
+    for (size_t j = 0; j < SCREEN_HEIGHT; j++) {
+        if (dirty_lines[j] == 1) {
+            for (size_t i = 0; i < SCREEN_WIDTH; i++) {
+                size_t idx = i + j * SCREEN_WIDTH;
+                framebuffer[idx] = palette[p->pixels[idx]];
+            }
+        }
+        dirty_lines[j] = 0;
+    }
+    reqdraw = 0;
+}