display now only draws chipxels that have changed

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",
@@ -36,30 +41,52 @@ DisplaySDL::~DisplaySDL() {
 }
 
 void DisplaySDL::clear() {
-  Display::clear();
+  for(auto &scanline : *mpFramebuffer) {
-  SDL_FillRect(SDL_GetWindowSurface(mpWindow), nullptr, mBgColor);
+    scanline.reset();
-  SDL_UpdateWindowSurface(mpWindow);
+  }
-  miTopDirtyScanline = chocochip8::gcHeight - 1;
+  mDoClear = true;
-  miBottomDirtyScanline = 0;
 }
 
-void DisplaySDL::updateWindow() const {
+int DisplaySDL::blit(const chocochip8::Scanline &spriteScanline, int y) {
-  if(miTopDirtyScanline > miBottomDirtyScanline) {
+  using chocochip8::Scanline;
-    // No changes since the last update
+  Scanline &targetScanline = mpFramebuffer->at(y);
-    return;
+  bool collision = (spriteScanline & targetScanline).any();
+  targetScanline ^= spriteScanline;
+  return collision;
 }
 
+void DisplaySDL::updateWindow(bool doWindowUpdate) const {
+  using chocochip8::Scanline;
   SDL_Surface *pSurface = SDL_GetWindowSurface(mpWindow);
-  for(int y = 0; y < chocochip8::gcHeight; y++) {
+  if(mDoClear) {
-    if(y < miTopDirtyScanline || miBottomDirtyScanline < y) {
+    for(auto &scanline : *mpDisplayState) {
+      scanline.reset();
+    }
+    SDL_FillRect(pSurface, NULL, mBgColor);
+    mDoClear = false;
+    doWindowUpdate = true;
+  }
+
+  for(int y = 0; y < mpFramebuffer->size(); y++) {
+    Scanline &rNewScanline = (*mpFramebuffer)[y];
+    Scanline &rOldScanline = (*mpDisplayState)[y];
+    if(rNewScanline == rOldScanline) {
       // Skip scanlines that haven't changed since the last update
       continue;
     }
 
-    for(int x = 0; x < chocochip8::gcWidth; x++) {
+    for(int x = 0; x < rNewScanline.size(); x++) {
-      // Map framebuffer pixel to SDL surface rectangle
+      bool isSet = rNewScanline._Unchecked_test(x);
-      int x1 = (      x * pSurface->w) / chocochip8::gcWidth;
+      bool wasSet = rOldScanline._Unchecked_test(x);
-      int x2 = ((x + 1) * pSurface->w) / chocochip8::gcWidth;
+      if(isSet == wasSet) {
+        continue;
+      }
+
+      // Map framebuffer pixel to SDL surface rectangle,
+      // note that the MSB of an scanline's bitset is the leftmost pixel.
+      int z = (chocochip8::gcWidth - 1) - x;
+      int x1 = (      z * pSurface->w) / chocochip8::gcWidth;
+      int x2 = ((z + 1) * pSurface->w) / chocochip8::gcWidth;
       int y1 = (      y * pSurface->h) / chocochip8::gcHeight;
       int y2 = ((y + 1) * pSurface->h) / chocochip8::gcHeight;
       SDL_Rect rect;
@@ -68,14 +95,14 @@ void DisplaySDL::updateWindow() const {
       rect.w = x2 - x1;
       rect.h = y2 - y1;
 
-      // Read Chocochip8 Framebuffer and choose appropriate color,
+      Uint32 color = (isSet ? mFgColor : mBgColor);
-      // note that the MSB of an scanline's bitset is the leftmost pixel.
-      Uint32 color = (mpFramebuffer->at(y)[(chocochip8::gcWidth - 1) - x] ? mFgColor : mBgColor);
       SDL_FillRect(pSurface, &rect, color);
+      doWindowUpdate = true;
     }
   }
 
-  miTopDirtyScanline = chocochip8::gcHeight - 1;
+  if(doWindowUpdate) {
-  miBottomDirtyScanline = 0;
+    *mpDisplayState = *mpFramebuffer;
     SDL_UpdateWindowSurface(mpWindow);
   }
+}

DisplaySDL.hpp

@@ -2,7 +2,9 @@
 
 #include "Peripherals.hpp"
 
+#include <array>
 #include <cstdint>
+#include <memory>
 #include <SDL2/SDL_video.h>
 
 class DisplaySDL : public chocochip8::Display {
@@ -10,10 +12,15 @@ public:
   DisplaySDL(int w, int h, uint32_t fgCol = 0xffffff, uint32_t bgCol = 0x000000);
   ~DisplaySDL() override;
   void clear() override;
-  void updateWindow() const;
+  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

@@ -290,12 +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.getModifyableScanline(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

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,
@@ -20,32 +17,9 @@ namespace chocochip8 {
 
   class Display {
   public:
-    Display():
-      mpFramebuffer{std::make_unique<Framebuffer>()},
-      miTopDirtyScanline{0},
-      miBottomDirtyScanline{gcHeight - 1} {}
-
     virtual ~Display() = default;
-
+    virtual int blit(const Scanline& spriteScanline, int y) = 0;
-    virtual void clear() {
+    virtual void clear() = 0;
-      for(auto &scanline : *mpFramebuffer) {
-        scanline.reset();
-      }
-      miTopDirtyScanline = 0;
-      miBottomDirtyScanline = gcHeight - 1;
-    }
-
-    virtual Scanline& getModifyableScanline(size_t y) {
-      Scanline& res = mpFramebuffer->at(y);
-      miTopDirtyScanline = std::min(miTopDirtyScanline, y);
-      miBottomDirtyScanline = std::max(miBottomDirtyScanline, y);
-      return res;
-    }
-
-  protected:
-    std::unique_ptr<Framebuffer> mpFramebuffer;
-    mutable size_t miTopDirtyScanline;
-    mutable size_t miBottomDirtyScanline;
   };
 
   class Buzzer {

main.cpp

@@ -9,8 +9,8 @@
 #include "DisplaySDL.hpp"
 #include "Interpreter.hpp"
 #include "Peripherals.hpp"
-#include "SDL_events.h"
+#include "SDL2/SDL_events.h"
-#include "SDL_timer.h"
+#include "SDL2/SDL_timer.h"
 
 int main(int argc, char* argv[]) {
   if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {