Check the total GPU memory usage from the card as well as our computed memory usage

libraries/gpu-gl/src/gpu/gl/GLBackend.cpp

@@ -39,6 +39,10 @@ static GLBackend* INSTANCE{ nullptr };
 static const char* GL_BACKEND_PROPERTY_NAME = "com.highfidelity.gl.backend";
 
 BackendPointer GLBackend::createBackend() {
+    // The ATI memory info extension only exposes 'free memory' so we want to force it to 
+    // cache the value as early as possible
+    getDedicatedMemory();
+
     // FIXME provide a mechanism to override the backend for testing
     // Where the gpuContext is initialized and where the TRUE Backend is created and assigned
     auto version = QOpenGLContextWrapper::currentContextVersion();

libraries/gpu-gl/src/gpu/gl/GLShared.cpp

@@ -60,6 +60,32 @@ bool checkGLErrorDebug(const char* name) {
 #endif
 }
 
+gpu::Size getFreeDedicatedMemory() {
+    Size result { 0 };
+    static bool nvidiaMemorySupported { true };
+    static bool atiMemorySupported { true };
+    if (nvidiaMemorySupported) {
+        
+        GLint nvGpuMemory { 0 };
+        glGetIntegerv(GL_GPU_MEMORY_INFO_CURRENT_AVAILABLE_VIDMEM_NVX, &nvGpuMemory);
+        if (GL_NO_ERROR == glGetError()) {
+            result = KB_TO_BYTES(nvGpuMemory);
+        } else {
+            nvidiaMemorySupported = false;
+        }
+    } else if (atiMemorySupported) {
+        GLint atiGpuMemory[4];
+        // not really total memory, but close enough if called early enough in the application lifecycle
+        glGetIntegerv(GL_TEXTURE_FREE_MEMORY_ATI, atiGpuMemory);
+        if (GL_NO_ERROR == glGetError()) {
+            result = KB_TO_BYTES(atiGpuMemory[0]);
+        } else {
+            atiMemorySupported = false;
+        }
+    }
+    return result;
+}
+
 gpu::Size getDedicatedMemory() {
     static Size dedicatedMemory { 0 };
     static std::once_flag once;

libraries/gpu-gl/src/gpu/gl/GLShared.h

@@ -25,6 +25,7 @@ void serverWait();
 void clientWait();
 
 gpu::Size getDedicatedMemory();
+gpu::Size getFreeDedicatedMemory();
 ComparisonFunction comparisonFuncFromGL(GLenum func);
 State::StencilOp stencilOpFromGL(GLenum stencilOp);
 State::BlendOp blendOpFromGL(GLenum blendOp);

libraries/gpu-gl/src/gpu/gl/GLTexture.cpp

@@ -92,6 +92,7 @@ const std::vector<GLenum>& GLTexture::getFaceTargets(GLenum target) {
     return faceTargets;
 }
 
+#define MIN_FREE_GPU_MEMORY_PERCENTAGE 0.25f
 float GLTexture::getMemoryPressure() {
     // Check for an explicit memory limit
     auto availableTextureMemory = Texture::getAllowedGPUMemoryUsage();
@@ -100,10 +101,19 @@ float GLTexture::getMemoryPressure() {
     if (!availableTextureMemory) {
         auto totalGpuMemory = getDedicatedMemory();
 
-        // If no limit has been explicitly set, and the dedicated memory can't be determined, 
-        // just use a fallback fixed value of 256 MB
         if (!totalGpuMemory) {
+            // If we can't query the dedicated memory just use a fallback fixed value of 256 MB
             totalGpuMemory = MB_TO_BYTES(DEFAULT_MAX_MEMORY_MB);
+        } else {
+            // Check the global free GPU memory
+            auto freeGpuMemory = getFreeDedicatedMemory();
+            if (freeGpuMemory) {
+                auto freePercentage = (float)freeGpuMemory / (float)totalGpuMemory;
+                if (freePercentage < MIN_FREE_GPU_MEMORY_PERCENTAGE) {
+                    qDebug() << "Exceeded max GPU memory";
+                    return 2.0;
+                }
+            }
         }
 
         // Allow 75% of all available GPU memory to be consumed by textures