BUGFIX: Collision works better, not 100%

BUGFIX: Video Reset works.

gemma/src/chip8/instructions.rs

@@ -673,30 +673,29 @@ impl Chip8CpuInstructions {
                 //     it wraps around to the opposite side of the screen.
 
                 let source_memory_offset = input.registers.peek_i();
-
                 let x_offset = input.registers.peek(*x as u8);
                 let y_offset = input.registers.peek(*y as u8);
 
-                debug!("X_OFFSET = {x_offset} / y_offset = {y_offset}");
-                let target_memory_offset = x_offset as u16 * 64 + y_offset as u16;
 
-                debug!("CHIP8CPUINSTRUCTION:DRAWVXNIBBLE -> STARTING AT {source_memory_offset} WRITING TO {target_memory_offset}");
+             //   let target_memory_offset = x_offset as u16 * 64 + y_offset as u16;
+
                 let num_bytes_to_read = *n;
-                debug!("CHIP8CPUINSTRUCTION:DRAWVXNIBBLE -> PREPARING TO READ {num_bytes_to_read} BYTES FROM MEMORY TO VIDEO");
+                let mut did_change = false;
+
                 for byte_index in 0..num_bytes_to_read {
                     let current_byte = input.memory.peek(byte_index as u16 + source_memory_offset);
-                    debug!("CHIP8CPUINSTRUCTION:DRAWVXNIBBLE -> READ BYTE [0x{byte_index:2x}]\t{current_byte:02x}\t{current_byte:08b}");
                     for bit_index in 0..8 {
                         let data_offset = ((x_offset as u16 + byte_index as u16) * 64) + (y_offset as u16 + bit_index as u16) as u16;
-                        let current_bit = (current_byte.shr(7 - bit_index) & 0x1u8) == 0x1u8;
+                        let current_bit = (current_byte & (0x80 >> bit_index)) != 0;
+                        let previous_bit = input.video_memory.peek(data_offset);
+                        let new_bit = previous_bit ^ current_bit;
+                        if previous_bit && !new_bit {
+                            did_change = true;
+                        }
                         input.video_memory.poke(data_offset, current_bit);
                     }
                 }
 
-                debug!("PPOOSSTT -> CHIP8CPUINSTRUCTION:DRAWVXNIBBLE -> {}", input.video_memory.format_as_string());
-
-                let mut did_change: bool = input.video_memory.has_frame_changed;
-
                 if did_change {
                     input.registers.poke(0xf, 1u8);
                 } else {

gemma/src/chip8/video.rs

@@ -8,16 +8,9 @@ pub struct Chip8Video {
 }
 
 impl Chip8Video {
-    fn int_cls(&self) -> Chip8Video {
-        let mut x = Chip8Video::default();
-        for i in 0..CHIP8_VIDEO_WIDTH {
-            x.poke(i as u16, false);
-        }
-        x
-    }
-
-    pub fn reset(&mut self) -> Self {
-        self.int_cls()
+    pub fn reset(&mut self) {
+        self.cls();
+        self.start_frame();
     }
 
     pub fn cls(&mut self) {
@@ -38,10 +31,15 @@ impl Chip8Video {
     }
 
     pub fn peek(self, address: u16) -> bool {
-        self.memory[address as usize]
+        let effective_address = if address >= 2048 {
+            address - 2048
+        } else {
+            address
+        };
+        self.memory[effective_address as usize]
     }
 
-    pub fn poke(&mut self, address: u16, new_value: bool) -> Self {
+    pub fn poke(&mut self, address: u16, new_value: bool) {
         // println!("OFFSET: {address} - POKING {new_value}");
 
         // Loop the address
@@ -56,12 +54,14 @@ impl Chip8Video {
         let value_changed = old_value != xored_value;  // From True to False is a change.
 
         self.has_frame_changed = if xored_value && value_changed { false } else { true };
+        if value_changed {
+            self.has_frame_changed = true;
+        }
 
         self.memory[effective_address as usize] = xored_value;
-        self.to_owned()
     }
 
-    pub fn poke_byte(&mut self, first_address: u16, to_write: u8) -> Self {
+    pub fn poke_byte(&mut self, first_address: u16, to_write: u8) {
         for i in (0..8).rev() {
             let shifted = ((1 << i) & to_write) >> i;
             //
@@ -69,7 +69,6 @@ impl Chip8Video {
             let is_set = shifted == 1;
             self.poke(target_address, is_set);
         }
-        self.to_owned()
     }
 
     pub fn poke_sprite(&mut self, first_address: u16, to_write: Vec<u8>) -> Self {
@@ -421,7 +420,7 @@ mod test {
             }
         }
 
-        x = x.reset();
+        x.reset();
         assert_eq!(x.format_as_string(), read_test_result("test_reset_clears_video.asc"));
     }
 
@@ -452,6 +451,17 @@ mod test {
 
         // now set a no-collision value
         x.poke_byte(0x00, 0b00001111);
-        assert_eq!(false, x.has_frame_changed);
+        assert_eq!(true, x.has_frame_changed);
+    }
+
+    #[test]
+    fn peek_out_of_bounds_doesnt_panic() {
+        let x = Chip8Video::default();
+
+        let y = x.peek(2049);
+        let y = x.peek(0);
+
+        // if we got here we didn't panic
+        assert!(true);
     }
 }

gemma/tests/computer_tests.rs

@@ -31,7 +31,7 @@ fn reset_clears_video() {
     }
 
     x.reset();
-    x.video_memory = x.video_memory.reset();
+    x.video_memory.reset();
 
     assert_eq!(x.dump_video_to_string(), x.video_memory.format_as_string());