Fix OpenGL quad texture coordinate handling

- Remove shader flip (1.0 - texcoord.y was incorrect)
- Set flipVertical = false (stb_image loads texture correctly as-is)
- Update GT.ppm with correct rendering output
- OpenGL quad now matches D3D12 GT exactly (0% diff)

engine/include/XCEngine/Audio/WASAPI/WASAPIBackend.h

@@ -5,6 +5,8 @@
 #include <vector>
 #include <thread>
 #include <atomic>
+#include <mutex>
+#include <condition_variable>
 
 #ifdef _WIN32
 #define NOMINMAX
@@ -86,6 +88,10 @@ private:
     std::vector<int16_t> m_audioBuffer2;
     bool m_isBuffer1Front = true;
     bool m_isBufferPrepared = false;
+    bool m_dataReady = false;
+
+    std::mutex m_bufferMutex;
+    std::condition_variable m_dataReadyCond;
 
     WAVEHDR m_waveHeader1 = {};
     WAVEHDR m_waveHeader2 = {};

engine/src/Audio/WASAPI/WASAPIBackend.cpp

@@ -141,9 +141,18 @@ void WASAPIBackend::ProcessAudio(float* buffer, uint32 bufferSize,
     }
 
     uint32 sampleCount = bufferSize / sizeof(float);
-    for (uint32 i = 0; i < sampleCount; ++i) {
-        buffer[i] *= volume;
+    int16_t* backBuffer = m_isBuffer1Front ? m_audioBuffer2.data() : m_audioBuffer1.data();
+    uint32 bufferSamples = static_cast<uint32>(m_audioBuffer1.size());
+
+    for (uint32 i = 0; i < sampleCount && i < bufferSamples; ++i) {
+        float sample = buffer[i] * volume;
+        sample = std::max(-1.0f, std::min(1.0f, sample));
+        backBuffer[i] = static_cast<int16_t>(sample * 32767.0f);
     }
+
+    std::lock_guard<std::mutex> lock(m_bufferMutex);
+    m_dataReady = true;
+    m_dataReadyCond.notify_one();
 }
 
 MMRESULT WASAPIBackend::InitDevice() {
@@ -204,7 +213,15 @@ void WASAPIBackend::AudioThread() {
     PlayFrontData();
 
     while (m_isRunning.load()) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+        std::unique_lock<std::mutex> lock(m_bufferMutex);
+        m_dataReadyCond.wait_for(lock, std::chrono::milliseconds(10), [this] { return m_dataReady || !m_isRunning.load(); });
+
+        if (m_dataReady) {
+            PrepareBackData();
+            SwapBuffer();
+            PlayFrontData();
+            m_dataReady = false;
+        }
     }
 }
 
@@ -236,11 +253,6 @@ MMRESULT WASAPIBackend::PlayFrontData() {
 }
 
 void WASAPIBackend::PrepareBackData() {
-    if (!m_isBufferPrepared) {
-        memset(m_audioBuffer1.data(), 0, m_audioBuffer1.size() * sizeof(int16_t));
-        memset(m_audioBuffer2.data(), 0, m_audioBuffer2.size() * sizeof(int16_t));
-        m_isBufferPrepared = true;
-    }
 }
 
 void WASAPIBackend::SwapBuffer() {