display now only draws chipxels that have changed

interpreter now passes Timendus' flags test

DisplaySDL.cpp

@@ -1,8 +1,13 @@
 #include "DisplaySDL.hpp"
+#include "Peripherals.hpp"
 
+#include <SDL2/SDL_surface.h>
 #include <stdexcept>
 
-DisplaySDL::DisplaySDL(int w, int h, uint32_t fgColor, uint32_t bgColor) {
+DisplaySDL::DisplaySDL(int w, int h, uint32_t fgColor, uint32_t bgColor):
+  mpFramebuffer{std::make_unique<Framebuffer>()},
+  mpDisplayState{std::make_unique<Framebuffer>()},
+  mDoClear{true} {
   // Create SDL Window
   mpWindow = SDL_CreateWindow(
     "ChocoChip-8",
@@ -35,43 +40,69 @@ DisplaySDL::~DisplaySDL() {
   SDL_DestroyWindow(mpWindow);
 }
 
-void DisplaySDL::updateWindow() const {
+void DisplaySDL::clear() {
+  for(auto &scanline : *mpFramebuffer) {
+    scanline.reset();
+  }
+  mDoClear = true;
+}
+
+int DisplaySDL::blit(const chocochip8::Scanline &spriteScanline, int y) {
+  using chocochip8::Scanline;
+  Scanline &targetScanline = mpFramebuffer->at(y);
+  bool collision = (spriteScanline & targetScanline).any();
+  targetScanline ^= spriteScanline;
+  return collision;
+}
+
+void DisplaySDL::updateWindow(bool doWindowUpdate) const {
+  using chocochip8::Scanline;
   SDL_Surface *pSurface = SDL_GetWindowSurface(mpWindow);
-  SDL_LockSurface(pSurface);
+  if(mDoClear) {
+    for(auto &scanline : *mpDisplayState) {
+      scanline.reset();
+    }
+    SDL_FillRect(pSurface, NULL, mBgColor);
+    mDoClear = false;
+    doWindowUpdate = true;
+  }
 
-  int fx, fy; // ChocoChip8 Framebuffer coordinates
+  for(int y = 0; y < mpFramebuffer->size(); y++) {
-  int sx, sy; // SDL Surface coordinates
+    Scanline &rNewScanline = (*mpFramebuffer)[y];
-  int lx, ly; // Last-used ChocoChip8 Framebuffer coordinates
+    Scanline &rOldScanline = (*mpDisplayState)[y];
-  Uint32 lc;  // Last-used SDL color
+    if(rNewScanline == rOldScanline) {
+      // Skip scanlines that haven't changed since the last update
+      continue;
+    }
 
-  // Fill the entire SDL surface, one pixel at a time
+    for(int x = 0; x < rNewScanline.size(); x++) {
-  lx = -1;
+      bool isSet = rNewScanline._Unchecked_test(x);
-  ly = -1;
+      bool wasSet = rOldScanline._Unchecked_test(x);
-  for(sy = 0; sy < pSurface->h; sy++) {
+      if(isSet == wasSet) {
-    for(sx = 0; sx < pSurface->w; sx++) {
+        continue;
-      // Map SDL surface coordinates to Chocochip8 Framebuffer coordinates
-      fx = sx * (double(chocochip8::gcWidth) / pSurface->w);
-      fy = sy * (double(chocochip8::gcHeight) / pSurface->h);
-
-      // Reuse color if this screen pixel maps to the same ChocoChip8 pixel as the last
-      if(fx != lx || fy != ly) {
-        lx = fx;
-        ly = ly;
-        // Read Chocochip8 Framebuffer and choose appropriate color,
-        // note that the MSB of an scanline's bitset is the leftmost pixel.
-        lc = (mpFramebuffer->at(fy)[(chocochip8::gcWidth - 1) - fx] ? mFgColor : mBgColor);
       }
 
-      // Convert (x, y) indexes into SDL Surface pixel array index
+      // Map framebuffer pixel to SDL surface rectangle,
-      Uint32 *pPixel = static_cast<Uint32*>(static_cast<void*>(
+      // note that the MSB of an scanline's bitset is the leftmost pixel.
-          static_cast<char*>(pSurface->pixels)
+      int z = (chocochip8::gcWidth - 1) - x;
-          + sy * pSurface->pitch
+      int x1 = (      z * pSurface->w) / chocochip8::gcWidth;
-          + sx * pSurface->format->BytesPerPixel
+      int x2 = ((z + 1) * pSurface->w) / chocochip8::gcWidth;
-      ));
+      int y1 = (      y * pSurface->h) / chocochip8::gcHeight;
-      *pPixel = lc;
+      int y2 = ((y + 1) * pSurface->h) / chocochip8::gcHeight;
+      SDL_Rect rect;
+      rect.x = x1;
+      rect.y = y1;
+      rect.w = x2 - x1;
+      rect.h = y2 - y1;
+
+      Uint32 color = (isSet ? mFgColor : mBgColor);
+      SDL_FillRect(pSurface, &rect, color);
+      doWindowUpdate = true;
     }
   }
 
-  SDL_UnlockSurface(pSurface);
+  if(doWindowUpdate) {
-  SDL_UpdateWindowSurface(mpWindow);
+    *mpDisplayState = *mpFramebuffer;
+    SDL_UpdateWindowSurface(mpWindow);
+  }
 }

DisplaySDL.hpp

@@ -2,17 +2,25 @@
 
 #include "Peripherals.hpp"
 
+#include <array>
 #include <cstdint>
+#include <memory>
 #include <SDL2/SDL_video.h>
 
 class DisplaySDL : public chocochip8::Display {
 public:
   DisplaySDL(int w, int h, uint32_t fgCol = 0xffffff, uint32_t bgCol = 0x000000);
   ~DisplaySDL() override;
-  void updateWindow() const;
+  void clear() override;
+  int blit(const chocochip8::Scanline &scanline, int y) override;
+  void updateWindow(bool forceWindowUpdate = false) const;
 
 private:
+  using Framebuffer = std::array<chocochip8::Scanline, chocochip8::gcHeight>;
+  std::unique_ptr<Framebuffer> mpFramebuffer;
+  mutable std::unique_ptr<Framebuffer> mpDisplayState;
   SDL_Window *mpWindow;
   Uint32 mFgColor;
   Uint32 mBgColor;
+  mutable bool mDoClear;
 };

Interpreter.cpp

@@ -4,6 +4,7 @@
 
 namespace chocochip8 {
 
+// converts any 8-bit sprite row to its high-res 16-bit equivalent
 constexpr uint16_t gcvLowResToHighResRowLookupTable[256] = {
   0x0000, 0x0003, 0x000C, 0x000F, 0x0030, 0x0033, 0x003C, 0x003F, 0x00C0, 0x00C3, 0x00CC, 0x00CF, 0x00F0, 0x00F3, 0x00FC, 0x00FF, 
   0x0300, 0x0303, 0x030C, 0x030F, 0x0330, 0x0333, 0x033C, 0x033F, 0x03C0, 0x03C3, 0x03CC, 0x03CF, 0x03F0, 0x03F3, 0x03FC, 0x03FF, 
@@ -23,6 +24,7 @@ constexpr uint16_t gcvLowResToHighResRowLookupTable[256] = {
   0xFF00, 0xFF03, 0xFF0C, 0xFF0F, 0xFF30, 0xFF33, 0xFF3C, 0xFF3F, 0xFFC0, 0xFFC3, 0xFFCC, 0xFFCF, 0xFFF0, 0xFFF3, 0xFFFC, 0xFFFF
 };
 
+// 4x5 sprites for hex digits 0-F
 constexpr uint8_t gcvLowResFontData[80] = {
   0xF0, 0x90, 0x90, 0x90, 0xF0,
   0x20, 0x60, 0x20, 0x20, 0x70,
@@ -68,8 +70,11 @@ void Interpreter::tick() {
   };
 
   // fetch instruction
-  sreg_t pc = mvSpecialReg[SR_PC];
+  sreg_t iInstAddr = mvSpecialReg[SR_PC];
-  unsigned inst = (mvMemory[pc] << 8) | mvMemory[pc + 1];
+  unsigned inst = (mvMemory.at(iInstAddr) << 8) | mvMemory.at(iInstAddr + 1);
+
+  // increment program counter
+  mvSpecialReg[SR_PC] += 2;
 
   // extract fields
   unsigned iRegDst = (inst & 0x0F00) >> 8; // destination register index
@@ -82,9 +87,7 @@ void Interpreter::tick() {
   case 0x0000: // 0NNN - call machine language routine
     switch(inst) {
     case 0x00E0: // clear display
-      for(auto &scanline : *mrDisplay.mpFramebuffer) {
+      mrDisplay.clear();
-        scanline.reset();
-      }
       break;
     case 0x00EE: // return from subroutine
       mvSpecialReg[SR_PC] = mCallStack.top();
@@ -99,7 +102,7 @@ void Interpreter::tick() {
     mvSpecialReg[SR_PC] = imm12;
     break;
   case 0x2000: // 2NNN - call subroutine
-    mCallStack.push(pc);
+    mCallStack.push(mvSpecialReg[SR_PC]);
     mvSpecialReg[SR_PC] = imm12;
     break;
   case 0x3000: // 3XNN - skip if equal immediate
@@ -138,12 +141,47 @@ void Interpreter::tick() {
   case 0xE000: // EX9E, EXA1 - keypad access
     break;
   case 0xF000: // several unique instructions
+    switch(inst & 0xF0FF) {
+    case 0xF007: // FX07 - read timer register
+      mvReg[iRegDst] = (mvSpecialReg[SR_T1] * scTimerFreq + (mcTicksPerSecond - 1)) / mcTicksPerSecond;
+      break;
+    case 0xF015: // FX15 - set timer register
+      mvSpecialReg[SR_T1] = (mcTicksPerSecond * mvReg[iRegDst]) / scTimerFreq;
+      break;
+    case 0xF018: // FX18 - set sound timer register
+      if(mvSpecialReg[SR_T2] == 0 && mvReg[iRegDst] != 0) {
+        mrBuzzer.on();
+      }
+      mvSpecialReg[SR_T2] = (mcTicksPerSecond * mvReg[iRegDst]) / scTimerFreq;
+      break;
+    case 0xF01E: // FX1E - add to I
+      mvSpecialReg[SR_I] += mvReg[iRegDst];
+      break;
+    case 0xF029: // FX29 - set I to address of font sprite data for digit X
+      mvSpecialReg[SR_I] = scLowRestFontAddr + 5 * mvReg[iRegDst];
+      break;
+    case 0xF033: // FX33 - convert to bcd
+      mvMemory.at(mvSpecialReg[SR_I])     = (mvReg[iRegDst] / 100) % 10;
+      mvMemory.at(mvSpecialReg[SR_I] + 1) = (mvReg[iRegDst] / 10) % 10;
+      mvMemory.at(mvSpecialReg[SR_I] + 2) = mvReg[iRegDst] % 10;
+      break;
+    case 0xF055: // FX55 - dump registers
+      for(int i = 0; i <= iRegDst - R_V0; i++) {
+        mvMemory.at(mvSpecialReg[SR_I]++) = mvReg[R_V0 + i];
+      }
+      break;
+    case 0xF065: // FX65 - restore registers
+      for(int i = 0; i <= iRegDst - R_V0; i++) {
+        mvReg[R_V0 + i] = mvMemory.at(mvSpecialReg[SR_I]++);
+      }
+      break;
+    default:
+      throw std::invalid_argument("not implemented");
+      break;
+    }
     break;
   }
 
-  // increment PC
-  mvSpecialReg[SR_PC] += 2;
-
   // decrement timers
   if(mvSpecialReg[SR_T1] > 0) {
     mvSpecialReg[SR_T1] -= 1;
@@ -172,27 +210,30 @@ void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
   case Opcode::XOR:  mvReg[iReg] ^= operand; break;
   case Opcode::RAND: mvReg[iReg]  = rand() & operand; break;
   case Opcode::LSH:
-    mvReg[R_VF] = (mvReg[iReg] & 0x80) ? 1 : 0;
+    mvReg[iReg] = operand << 1;
-    mvReg[iReg] <<= 1;
+    // VF = shifted out bit
+    mvReg[R_VF] = (operand & 0x80) ? 1 : 0;
     break;
   case Opcode::RSH:
-    mvReg[R_VF] = (mvReg[iReg] & 0x01) ? 1 : 0;
+    mvReg[iReg] = operand >> 1;
-    mvReg[iReg] >>= 1;
+    // VF = shifted out bit
+    mvReg[R_VF] = (operand & 0x01) ? 1 : 0;
     break;
   case Opcode::ADD:
-    tmp = mvReg[iReg] + operand;
+    mvReg[iReg] = mvReg[iReg] + operand;
-    mvReg[R_VF] = (tmp < mvReg[iReg]) ? 1 : 0;
+    // VF = 1 if carry occurs, VF = 0 if no carry
-    mvReg[iReg] = tmp;
+    mvReg[R_VF] = (mvReg[iReg] < operand) ? 1 : 0;
     break;
   case Opcode::SUB:
-    tmp = mvReg[iReg] - operand;
+    tmp = mvReg[iReg];
-    mvReg[R_VF] = (tmp > mvReg[iReg]) ? 1 : 0;
+    mvReg[iReg] = mvReg[iReg] - operand;
-    mvReg[iReg] = tmp;
+    // VF = 0 if borrow occurs, VF = 1 if no borrow
+    mvReg[R_VF] = (mvReg[iReg] > tmp) ? 0 : 1;
     break;
   case Opcode::SUB2:
-    tmp = operand - mvReg[iReg];
+    mvReg[iReg] = operand - mvReg[iReg];
-    mvReg[R_VF] = (tmp > operand) ? 1 : 0;
+    // VF = 0 if borrow occurs, VF = 1 if no borrow
-    mvReg[iReg] = tmp;
+    mvReg[R_VF] = (mvReg[iReg] > operand) ? 0 : 1;
     break;
   case Opcode::JEQ:
     if(mvReg[iReg] == operand) {
@@ -229,14 +270,14 @@ void Interpreter::executeDraw(uint8_t x, uint8_t y, uint8_t n) {
     uint16_t spriteRowBits;
     if(mIsHighResMode) {
       // draws an 8xN sprite
-      spriteRowBits = mvMemory[iMemAddr++] << 8;
+      spriteRowBits = mvMemory.at(iMemAddr++) << 8;
       if(n == 0) {
         // draws an 16xN sprite, so fetch another byte from sprite data
-        spriteRowBits |= mvMemory[iMemAddr++];
+        spriteRowBits |= mvMemory.at(iMemAddr++);
       }
     } else {
       // in low-res mode, each sprite pixel draws two on-screen pixels
-      spriteRowBits = gcvLowResToHighResRowLookupTable[mvMemory[iMemAddr++]];
+      spriteRowBits = gcvLowResToHighResRowLookupTable[mvMemory.at(iMemAddr++)];
     }
 
     // convert to bitset and shift into absolute horizontal position on the screen
@@ -249,12 +290,10 @@ void Interpreter::executeDraw(uint8_t x, uint8_t y, uint8_t n) {
 
     // we draw one scanline per sprite row in high-res mode, but twice in low-res mode
     for(int j = 0; j < (mIsHighResMode ? 1 : 2); j++) {
-      Scanline &targetScanline = mrDisplay.mpFramebuffer->at(y + i * (mIsHighResMode ? 1 : 2) + j);
+      // blit the sprite bitset into the screen
-      if((targetScanline & spriteScanline) != 0) {
+      if(mrDisplay.blit(spriteScanline, y + i * (mIsHighResMode ? 1 : 2) + j) != 0) {
         collisionCount += 1;
       }
-      // blit the sprite bitset into the screen
-      targetScanline ^= spriteScanline;
     }
 
     // update state flags

Interpreter.hpp

@@ -16,6 +16,7 @@ private:
 public:
   constexpr static sreg_t scLowRestFontAddr = 0x0000;
   constexpr static sreg_t scResetVector = 0x0200;
+  constexpr static sreg_t scTimerFreq = 60;
   constexpr static size_t scMemorySize = 4096;
 
   enum {

Peripherals.hpp

@@ -1,15 +1,12 @@
 #pragma once
 
-#include <array>
 #include <bitset>
-#include <memory>
 
 namespace chocochip8 {
 
   constexpr size_t gcWidth = 128;
   constexpr size_t gcHeight = 64;
   using Scanline = std::bitset<gcWidth>;
-  using Framebuffer = std::array<Scanline, gcHeight>;
 
   enum class Key {
     KEY_0, KEY_1, KEY_2, KEY_3,
@@ -20,11 +17,9 @@ namespace chocochip8 {
 
   class Display {
   public:
-    friend class Interpreter;
-    Display(): mpFramebuffer{std::make_unique<Framebuffer>()} {}
     virtual ~Display() = default;
-  protected:
+    virtual int blit(const Scanline& spriteScanline, int y) = 0;
-    std::unique_ptr<Framebuffer> mpFramebuffer;
+    virtual void clear() = 0;
   };
 
   class Buzzer {

main.cpp

@@ -1,12 +1,18 @@
 #include <iostream>
+#include <iterator>
+#include <fstream>
+#include <vector>
+
 #include <SDL2/SDL.h>
 
 #include "BuzzerSDL.hpp"
 #include "DisplaySDL.hpp"
 #include "Interpreter.hpp"
 #include "Peripherals.hpp"
+#include "SDL2/SDL_events.h"
+#include "SDL2/SDL_timer.h"
 
-int main(int argc, char* args[]) {
+int main(int argc, char* argv[]) {
   if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
     std::cerr << "Couldn't initialize SDL: " << SDL_GetError() << '\n';
     return 1;
@@ -19,35 +25,34 @@ int main(int argc, char* args[]) {
   BuzzerSDL buzzer(440);
   DisplaySDL display(1280, 640);
   TestKeypad keypad;
-  chocochip8::Interpreter chip8(90, display, buzzer, keypad);
+  chocochip8::Interpreter chip8(1000, display, buzzer, keypad);
 
-  uint8_t prog[] = {
+  auto rom = std::vector<char>();
-    0xA0, 0x00,  // LD I,0
+  auto romfile = std::ifstream(argv[1] != NULL ? argv[1] : "/dev/stdin", std::ios_base::in | std::ios_base::binary);
-    0x60, 0x00,  // LD $0,0
+  std::copy(
-    0x61, 0x00,  // LD $1,0
+    std::istreambuf_iterator<char>(romfile),
-    0xD0, 0x15,  // DRW $0, $1, 5
+    std::istreambuf_iterator<char>(),
-    0xA0, 0x05,  // LD I,5
+    std::back_insert_iterator(rom)
-    0x60, 0x3C,  // LD $0,60
+  );
-    0x61, 0x00,  // LD $1,0
+  chip8.loadProgram(rom.data(), rom.size());
-    0xD0, 0x15,  // DRW $0, $1, 5
-    0xA0, 0x0A,  // LD I,10
-    0x60, 0x00,  // LD $0,0
-    0x61, 0x1B,  // LD $1,27
-    0xD0, 0x15,  // DRW $0, $1, 5
-    0xA0, 0x0F,  // LD I,15
-    0x60, 0x3C,  // LD $0,60
-    0x61, 0x1B,  // LD $1,27
-    0xD0, 0x15,  // DRW $0, $1, 5
-  };
-
-  chip8.loadProgram((char*)prog, sizeof(prog));
-  for(int i = 0; i < sizeof(prog) / 2; i++) {
-    chip8.tick();
-  }
 
   SDL_Event event;
-  while(SDL_WaitEvent(&event) && event.type != SDL_QUIT) {
+  bool done = false;
+  Uint64 start, end;
+  start = SDL_GetTicks64();
+  while(!done) {
+    while(SDL_PollEvent(&event)) {
+      if(event.type == SDL_QUIT) {
+        done = true;
+      }
+    }
+    chip8.tick();
     display.updateWindow();
+    SDL_Delay(1);
+    end = SDL_GetTicks64();
+    if(end - start > 3) 
+      std::cout << "Frame took too long: " << end - start << "\n";
+    start = end;
   }
   
   buzzer.off();