From 215465df74a6065f4b0fdf199b8b04454520a398 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Wed, 2 Jun 2021 20:20:23 +0200
Subject: Update the renderer to support a text layer

---
 src/renderer.c | 71 +++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 48 insertions(+), 23 deletions(-)

(limited to 'src/renderer.c')

diff --git a/src/renderer.c b/src/renderer.c
index 9fe55b2..ec54411 100644
--- a/src/renderer.c
+++ b/src/renderer.c
@@ -1,14 +1,28 @@
-// TODO: For now we pack front/backbuffers together but this make it so that we
-// can only use 2 backgrounds. Instead we can move the backbuffer to the end of
-// the VRAM. This will give us 3 backgrounds but eats into the available memory
-// for sprites but should be fine for non sprite intensive applications.
-#define FRONTBUFFER ((u32*)(MEM_VRAM))
-#define BACKBUFFER  ((u32*)(MEM_VRAM + KB(96) - KB(20)))
+#include "bd-font.c"
+
+// The frontbuffer is located at the beginning of the VRAM, and requires 20KB of
+// video memory for 32 * 20 tiles at 4bpp.
+#define FRONTBUF ((u32*)(MEM_VRAM))
 
 // Adjust both of these if the location of the map changes. Each screnblock
-// requires 2K.
-#define FRONTBUFFER_TILEMAP     ((u16*)(MEM_VRAM + KB(20)))
-#define FRONTBUFFER_SCREENBLOCK 10
+// requires less than 2KB.
+#define FRONTBUF_TILEMAP ((u16*)(MEM_VRAM + KB(20)))
+#define FRONTBUF_SB      10
+
+// The backbuffer is located at the end of the VRAM. This can allow us to use
+// more backgrounds but eats into the available memory for sprites. This should
+// be fine for non sprite intensive applications. If more sprite memory is
+// needed, the backbuffer can be located at the end of the background memory
+// instead (64KB - 20KB).
+#define BACKBUF  ((u32*)(MEM_VRAM + KB(96) - KB(20)))
+
+// The font data is located at the end of the frontbuffer memory, after the tile
+// map and requires 8KB for 256 8x8 characters at 4bpp. This, along with the
+// tilemap information allow us to store the frontbuffer and font for a text
+// background in the first 2 charblocks (32KB).
+#define FONT_DATA    ((u32*)(MEM_VRAM + KB(22)))
+#define FONT_TILEMAP ((u16*)(MEM_VRAM + KB(30)))
+#define FONT_SB      15
 
 static u32 dirty_tiles[21] = {0};
 
@@ -29,7 +43,7 @@ draw_pixel(u16 x, u16 y, u8 color) {
 
     // Update backbuffer.
     size_t shift = start_col * sizeof(u32);
-    BACKBUFFER[pos] = (BACKBUFFER[pos] & ~(0xF << shift)) | color << shift;
+    BACKBUF[pos] = (BACKBUF[pos] & ~(0xF << shift)) | color << shift;
 
     // Mark tile as dirty.
     dirty_tiles[tile_y] |= 1 << tile_x;
@@ -39,8 +53,8 @@ IWRAM_CODE
 void
 flip_buffer(void) {
     // Copy dirty tiles from the backbuffer to the frontbuffer.
-    Tile *dst = FRONTBUFFER;
-    Tile *src = BACKBUFFER;
+    Tile *dst = FRONTBUF;
+    Tile *src = BACKBUF;
     for (size_t j = 0; j < 20; ++j) {
         if (dirty_tiles[j] == 0) {
             continue;
@@ -54,19 +68,23 @@ flip_buffer(void) {
     }
 }
 
+static u16 font_map[256] = {0};
+
 void
 renderer_init(void) {
     // Initialize display mode and bg palette.
-    DISP_CTRL = DISP_MODE_0 | DISP_BG_0 | DISP_OBJ;
+    DISP_CTRL = DISP_MODE_0 | DISP_BG_0 | DISP_BG_1 | DISP_OBJ;
 
     // Initialize backgrounds.
-    BG_CTRL(0) = BG_CHARBLOCK(0) | BG_SCREENBLOCK(FRONTBUFFER_SCREENBLOCK);
+    BG_CTRL(0) = BG_CHARBLOCK(0) | BG_SCREENBLOCK(FRONTBUF_SB) | BG_PRIORITY(1);
+    BG_CTRL(1) = BG_CHARBLOCK(1) | BG_SCREENBLOCK(FONT_SB) | BG_PRIORITY(0);
 
-    // TODO: Initialize other backgrounds if needed.
-
-    // Use DMA to clear front and back buffers.
-    dma_fill(FRONTBUFFER, 0, KB(20), 3);
-    dma_fill(BACKBUFFER, 0, KB(20), 3);
+    // Use DMA to clear front and back buffers as well as the font memory map.
+    dma_fill(FRONTBUF, 0, KB(20), 3);
+    dma_fill(FRONTBUF_TILEMAP, 0, KB(2), 3);
+    dma_fill(FONT_DATA, 0, KB(8), 3);
+    dma_fill(FONT_TILEMAP, 0, KB(2), 3);
+    dma_fill(BACKBUF, 0, KB(20), 3);
 
     // Initialize default palette.
     PAL_BUFFER_BG[0] = COLOR_BLACK;
@@ -76,11 +94,18 @@ renderer_init(void) {
     PAL_BUFFER_BG[4] = COLOR_CYAN;
     PAL_BUFFER_BG[5] = COLOR_GREY;
 
-    // Initialize background memory map.
+    // Initialize background memory map for frontbuffer and font backgorund.
     for (size_t i = 0; i < 32 * 20; ++i) {
-        FRONTBUFFER_TILEMAP[i] = i;
+        FRONTBUF_TILEMAP[i] = i;
     }
 
-//     // Load font data into VRAM.
-//     unpack_tiles(&bd_font, FONT_DATA, 256);
+    // Load font data into VRAM.
+    unpack_tiles(&bd_font, FONT_DATA, 256);
+
+    // Initialize the font map translation table. That way we can write
+    // a character on the text background layer with:
+    //     FONT_TILEMAP[tile_x + 32 * tile_y] = font_map['A'];
+    for (size_t i = 0; i < 256; ++i) {
+        font_map[i] = 192 + i;
+    }
 }
-- 
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