From 37a22f996620050fa7664413013315caa5b1d974 Mon Sep 17 00:00:00 2001
From: "Zed A. Shaw" <zed.shaw@gmail.com>
Date: Mon, 18 May 2026 12:52:51 -0400
Subject: [PATCH] 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 |  5 +++++
 src/chip8.hpp |  1 +
 src/main.cpp  | 16 +++++++++-------
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/chip8.cpp b/src/chip8.cpp
index 19ab816..d8e41ba 100644
--- a/src/chip8.cpp
+++ b/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() {
diff --git a/src/chip8.hpp b/src/chip8.hpp
index e205961..d5ad3ec 100644
--- a/src/chip8.hpp
+++ b/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;
diff --git a/src/main.cpp b/src/main.cpp
index ecdc702..8082bd8 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -99,13 +99,15 @@ int main(int argc, char* argv[]) {
     chip8.Cycle();
     cycle_stats.sample_time(t);
 
-    auto ut = update_stats.time_start();
-    display.update(chip8);
-    update_stats.sample_time(ut);
-
-    auto rt = render_stats.time_start();
-    display.render();
-    render_stats.sample_time(rt);
+    if(chip8.needs_render) {
+      auto ut = update_stats.time_start();
+      display.update(chip8);
+      update_stats.sample_time(ut);
+
+      auto rt = render_stats.time_start();
+      display.render();
+      render_stats.sample_time(rt);
+    }
   }
 
   cycle_stats.dump("CYCLE TIMES");