Little optimization where I don't render if there was a colision. This is because chip-8 attempts to draw to detect colision, and then 'undoes' it, so no point in rendering that.

src/chip8.cpp

@@ -288,8 +288,10 @@ void Chip8::OP_Dxyn() {
   uint8_t yPos = registers[Vy] % VIDEO_HEIGHT;
 
   registers[0xF] = 0;
+
   for(size_t row = 0; row < height; ++row) {
     uint8_t spriteByte = memory[index + row];
+
     for(size_t col = 0; col < 8; ++col) {
       uint8_t spritePixel = spriteByte & (0x80u >> col);
       uint32_t* screenPixel = &video[(yPos + row) * VIDEO_WIDTH + (xPos + col)];
@@ -305,6 +307,9 @@ void Chip8::OP_Dxyn() {
       }
     }
   }
+
+  // don't bother rendering collision tests
+  needs_render = !registers[0xF];
 }
 
 void Chip8::OP_Ex9E() {

src/chip8.hpp

@@ -45,6 +45,7 @@ class Chip8 {
       0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
       0xF0, 0x80, 0xF0, 0x80, 0x80  // F
     };
+    bool needs_render = true;
 
     std::default_random_engine randGen;
     std::uniform_int_distribution<uint8_t> randByte;

src/main.cpp

@@ -99,6 +99,7 @@ int main(int argc, char* argv[]) {
     chip8.Cycle();
     cycle_stats.sample_time(t);
 
+    if(chip8.needs_render) {
       auto ut = update_stats.time_start();
       display.update(chip8);
       update_stats.sample_time(ut);
@@ -107,6 +108,7 @@ int main(int argc, char* argv[]) {
       display.render();
       render_stats.sample_time(rt);
     }
+  }
 
   cycle_stats.dump("CYCLE TIMES");
   update_stats.dump("UPDATE TIMES");