From: John Tsiombikas <nuclear@member.fsf.org>
Date: Tue, 15 Dec 2020 02:13:28 +0000 (+0200)
Subject: RLE blitter, plus RLE encoding and decoding tools
X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootsplash;a=commitdiff_plain;h=5731d2abe8e8c4b838f8d1b0eefdc25754f6ad78

RLE blitter, plus RLE encoding and decoding tools
---

diff --git a/.gitignore b/.gitignore
index d9e3493..492e4f8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,10 @@
 *.swp
+*.o
 *.bin
 *.img
+*.pgm
+*.log
+*.rle
+dis
+rle/rle
+rle/unrle
diff --git a/Makefile b/Makefile
index a9d1f17..2ae07cf 100644
--- a/Makefile
+++ b/Makefile
@@ -5,9 +5,12 @@ $(img): $(bin)
 	dd if=/dev/zero of=$@ bs=512 count=2880
 	dd if=$< of=$@ bs=512 conv=notrunc
 
-$(bin): bootsplash.asm
+$(bin): bootsplash.asm nuclear.rle
 	nasm -f bin -o $@ $<
 
+nuclear.rle: nuclear.img
+	cat $< | rle/rle >$@ 2>rle.log
+
 .PHONY: run
 run: $(img)
 	qemu-system-i386 -fda $<
@@ -15,3 +18,7 @@ run: $(img)
 .PHONY: debug
 debug: $(img)
 	qemu-system-i386 -S -s -fda $<
+
+.PHONY: disasm
+disasm: $(bin)
+	ndisasm -o 0x7c00 $< >dis
diff --git a/bootsplash.asm b/bootsplash.asm
index e8c4cc7..a6a552a 100644
--- a/bootsplash.asm
+++ b/bootsplash.asm
@@ -61,6 +61,7 @@ stage2_start:
 
 	xor ax, ax
 	mov es, ax
+	mov ds, ax
 
 	mov ax, str_booting
 	call printstr
@@ -69,6 +70,7 @@ stage2_start:
 .hang:	hlt
 	jmp .hang
 
+	; splash screen effect
 splash:
 	mov ax, 13h
 	int 10h
@@ -76,14 +78,45 @@ splash:
 	mov ax, 0a000h
 	mov es, ax
 	xor di, di
-	mov cx, 32000
-	mov ax, 0505h
-	rep stosw
+
+	mov ax, pic
+	shr ax, 4
+	mov ds, ax
+	xor si, si
+
+	mov cx, 64000
+	call decode_rle
 
 	call waitkey
 
 	mov ax, 3
 	int 10h
+	ret
+
+	; decode RLE from ds:si to es:di, cx: number of decoded bytes (0 means 65536)
+	; - high bit set for the repetition count, followed by a value byte to
+	;   be repeated N times
+	; - high bit not set for raw data that should be copied directly
+decode_rle:
+	mov al, [si]
+	inc si
+	mov bl, 1	; default to "copy once" for raw values
+	test al, 0x80	; test the high bit to see if it's a count or a raw value
+	jz .copy
+	; it's a count, clear the high bit, and read the next byte for the value
+	and al, 0x7f
+	mov bl, al
+	mov al, [si]
+	inc si
+.copy:	mov [es:di], al
+	inc di
+	dec cx		; decrement decoded bytes counter
+	jz .end		; as soon as it reaches 0, bail
+	dec bl
+	jnz .copy
+	jmp decode_rle
+.end:	ret
+	
 
 waitkey:
 	in al, 64h
@@ -92,6 +125,10 @@ waitkey:
 	in al, 60h
 	ret
 
+	; data
+	align 16
+pic:	incbin "nuclear.rle"
+
 stage2_end:
 
 ; vi:set ft=nasm:
diff --git a/rle/Makefile b/rle/Makefile
new file mode 100644
index 0000000..1d50a5b
--- /dev/null
+++ b/rle/Makefile
@@ -0,0 +1,13 @@
+all: rle unrle
+
+rle: rle.o
+	$(CC) -o $@ $< $(LDFLAGS)
+
+unrle: unrle.o
+	$(CC) -o $@ $< $(LDFLAGS)
+
+clean:
+	$(RM) rle.o
+	$(RM) rle
+	$(RM) unrle.o
+	$(RM) unrle
diff --git a/rle/rle.c b/rle/rle.c
new file mode 100644
index 0000000..4acb24c
--- /dev/null
+++ b/rle/rle.c
@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void emit(int c, int count);
+
+int main(void)
+{
+	int c, lastc, count;
+
+	lastc = -1;
+	count = 0;
+
+	while((c = getchar()) != -1) {
+		if(c == lastc && count < 127) {
+			count++;
+		} else {
+			emit(lastc, count);
+			count = 1;
+			lastc = c;
+		}
+	}
+	emit(lastc, count);
+
+	return 0;
+}
+
+void emit(int c, int count)
+{
+	if(count <= 0 || c < 0) return;
+
+	fprintf(stderr, "emit(%d, %d) -> ", c, count);
+	if(count > 2 || (c & 0x80)) {
+		fprintf(stderr, "%02x %02x\n", (unsigned int)count | 0x80, (unsigned int)c);
+		putchar(count | 0x80);
+		putchar(c);
+	} else {
+		while(count--) {
+			fprintf(stderr, "%02x\n", (unsigned int)c & 0x7f);
+			putchar(c);
+		}
+	}
+}
diff --git a/rle/unrle.c b/rle/unrle.c
new file mode 100644
index 0000000..7f70edd
--- /dev/null
+++ b/rle/unrle.c
@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+int main(void)
+{
+	int c, count, rawbytes = 0;
+
+	printf("P5\n320 200\n255\n");
+
+	while((c = getchar()) != -1) {
+		if(c & 0x80) {
+			count = c & 0x7f;
+			if((c = getchar()) == -1) {
+				fprintf(stderr, "Unexpected EOF while decoding RLE data\n");
+				return 1;
+			}
+			rawbytes += count;
+			while(count--) putchar(c);
+		} else {
+			rawbytes++;
+			putchar(c);
+		}
+	}
+
+	fprintf(stderr, "decoded (raw) size: %d bytes\n", rawbytes);
+	return 0;
+}