now the display can draw sprites

Makefile

@@ -3,7 +3,8 @@ ECHO=echo -e
 CFLAGS=-Wall -Werror -std=gnu99 -O0 -g -Iinclude
 LIBS=-lSDL2
 
-FILES=build/main.o build/mem.o build/stack.o build/keyboard.o build/chip8.o
+FILES=build/main.o build/mem.o build/stack.o build/keyboard.o build/chip8.o \
+			build/screen.o
 OUT=bin/chip8.out
 
 all: $(FILES)
@@ -30,6 +31,10 @@ build/chip8.o: src/chip8.c
 	@$(ECHO) "CC\t\t"$<
 	@$(CC) $(CFLAGS) $< -c -o $@ $(LIBS)
 
+build/screen.o: src/screen.c
+	@$(ECHO) "CC\t\t"$<
+	@$(CC) $(CFLAGS) $< -c -o $@ $(LIBS)
+
 run: all
 	@$(ECHO) "Runing the Chip8 compiler"
 	@$(OUT)

include/chip8.h

@@ -5,6 +5,7 @@
 #include "keyboard.h"
 #include "mem.h"
 #include "registers.h"
+#include "screen.h"
 #include "stack.h"
 
 struct chip8
@@ -13,6 +14,7 @@ struct chip8
 	struct chip8_registers registers;
 	struct chip8_stack stack;
 	struct chip8_keyboard keyboard;
+	struct chip8_screen screen;
 };
 
 void chip8_init (struct chip8 *chip8);

include/config.h

@@ -5,7 +5,8 @@
 #define EMULATOR_WINDOW_MULTIPLIER 10
 
 #define CHIP8_MEMORY_SIZE 4096
-#define CHIP8_DISPLAY_WIDTH 63
+
+#define CHIP8_DISPLAY_WIDTH 64
 #define CHIP8_DISPLAY_HEIGHT 32
 
 #define CHIP8_TOTAL_DATA_REGISTERS 16

include/screen.h

@@ -0,0 +1,16 @@
+#ifndef __SCREEN_H
+#define __SCREEN_H
+
+#include "config.h"
+
+struct chip8_screen
+{
+	_Bool pixels[CHIP8_DISPLAY_HEIGHT][CHIP8_DISPLAY_WIDTH];
+};
+
+void chip8_screen_set (struct chip8_screen *screen, int x, int y);
+_Bool chip8_screen_is_set (struct chip8_screen *screen, int x, int y);
+_Bool chip8_screen_draw_sprite (struct chip8_screen *screen, int x, int y,
+																const char *sptr, int num);
+
+#endif

src/main.c

@@ -11,6 +11,8 @@ main (int argc, char **argv)
 {
 	struct chip8 chip8;
 	chip8_init (&chip8);
+	chip8_screen_draw_sprite (&chip8.screen, 62, 10,
+														(const char *)&chip8.memory.memory[0x00], 5);
 
 	SDL_Init (SDL_INIT_EVERYTHING);
 	SDL_Window *window = SDL_CreateWindow (
@@ -57,10 +59,23 @@ main (int argc, char **argv)
 
 			SDL_SetRenderDrawColor (renderer, 0, 0, 0, 0);
 			SDL_RenderClear (renderer);
-
 			SDL_SetRenderDrawColor (renderer, 255, 255, 255, 0);
-			SDL_Rect r = { 0, 0, 40, 40 };
+
-			SDL_RenderFillRect (renderer, &r);
+			for (int x = 0; x < CHIP8_DISPLAY_WIDTH; x++)
+				{
+					for (int y = 0; y < CHIP8_DISPLAY_HEIGHT; y++)
+						{
+							if (chip8_screen_is_set (&chip8.screen, x, y))
+								{
+									SDL_Rect r = { 0 };
+									r.x = x * EMULATOR_WINDOW_MULTIPLIER;
+									r.y = y * EMULATOR_WINDOW_MULTIPLIER;
+									r.w = EMULATOR_WINDOW_MULTIPLIER;
+									r.h = EMULATOR_WINDOW_MULTIPLIER;
+									SDL_RenderFillRect (renderer, &r);
+								}
+						}
+				}
 
 			SDL_RenderPresent (renderer);
 		}

src/screen.c

@@ -0,0 +1,54 @@
+#include "screen.h"
+
+#include <assert.h>
+
+static void
+chip8_screen_ensure_in_bounds (int x, int y)
+{
+	assert (x >= 0 && x <= CHIP8_DISPLAY_WIDTH);
+	assert (y >= 0 && y <= CHIP8_DISPLAY_HEIGHT);
+}
+
+void
+chip8_screen_set (struct chip8_screen *screen, int x, int y)
+{
+	chip8_screen_ensure_in_bounds (x, y);
+	screen->pixels[y][x] = 1;
+}
+
+_Bool
+chip8_screen_is_set (struct chip8_screen *screen, int x, int y)
+{
+	chip8_screen_ensure_in_bounds (x, y);
+	return screen->pixels[y][x];
+}
+
+_Bool
+chip8_screen_draw_sprite (struct chip8_screen *screen, int x, int y,
+													const char *sptr, int num)
+{
+	_Bool sprite_hit = 0; // true if sptr overrides a set bit
+
+	for (int ly = 0; ly < num; ly++)
+		{
+			char c = sptr[ly];
+			for (int lx = 0; lx < 8; lx++)
+				{
+					if ((c & (0b10000000 >> lx)) == 0)
+						continue;
+
+					if (screen->pixels[(ly + y) % CHIP8_DISPLAY_HEIGHT]
+														[(lx + x) % CHIP8_DISPLAY_WIDTH])
+						{
+							sprite_hit = 1;
+						}
+
+					// the % wraps it around the screen
+					screen->pixels[(ly + y) % CHIP8_DISPLAY_HEIGHT]
+												[(lx + x) % CHIP8_DISPLAY_WIDTH]
+							^= 1;
+				}
+		}
+
+	return sprite_hit;
+}