Cache isMSAASwapChainSupported() result for EGL

filament/backend/include/backend/platforms/PlatformEGL.h

@@ -28,6 +28,7 @@
 #include <utils/Invocable.h>
 
 #include <initializer_list>
+#include <optional>
 #include <utility>
 #include <vector>
 
@@ -168,6 +169,9 @@ class PlatformEGL : public OpenGLPlatform {
     EGLConfig mEGLConfig = EGL_NO_CONFIG_KHR;
     Config mContextAttribs;
     std::vector<EGLContext> mAdditionalContexts;
+    // A cache for MSAA support queries. The index of the vector corresponds to the power of 2 of
+    // the sample count. For example, index 0 is for 2 samples, 1 is for 4 samples, etc.
+    mutable std::vector<std::optional<bool>> mMSAASupport{4}; // caches for 2x, 4x, 8x, 16x
 
     // supported extensions detected at runtime
     struct {

filament/backend/src/opengl/platforms/PlatformEGL.cpp

@@ -32,6 +32,7 @@
 #endif
 #include <utils/compiler.h>
 
+#include <utils/algorithm.h>
 #include <utils/Invocable.h>
 #include <utils/Logger.h>
 #include <utils/debug.h>
@@ -491,14 +492,35 @@ bool PlatformEGL::isMSAASwapChainSupported(uint32_t samples) const noexcept {
         return true;
     }
 
+    // The number of samples must be a power-of-two > 1.
+    if ((samples & (samples - 1)) != 0) {
+        LOG(INFO) << "The number of samples for MSAA is not a power of two: " << samples;
+        return false;
+    }
+
+    // `samples` is a power-of-two that is greater than 1 (e.g., 2, 4, 8, ...).
+    // We use this to compute an index into our cache.
+    const uint32_t power = utils::ctz(samples); // `power` is 3 if the number of samples is 8x.
+    const uint32_t index = power - 1; // The index 0 originally means 1x, which we don't count.
+                                      // So make the index 0 to indicate 2x.
+    if (mMSAASupport.size() <= index) {
+        mMSAASupport.resize(index + 1);
+    }
+
+    // Return the cached value if we have one.
+    if (mMSAASupport[index]) {
+        return *mMSAASupport[index];
+    }
+
+    // Retrieve the config to see if the given number of samples is supported. The result is cached.
     Config configAttribs = {
             { EGL_SURFACE_TYPE,    EGL_WINDOW_BIT | EGL_PBUFFER_BIT },
             { EGL_RED_SIZE,        8 },
             { EGL_GREEN_SIZE,      8 },
             { EGL_BLUE_SIZE,       8 },
             { EGL_DEPTH_SIZE,      24 },
             { EGL_SAMPLE_BUFFERS,  1 },
-            { EGL_SAMPLES,         samples },
+            { EGL_SAMPLES,         (EGLint)samples },
     };
 
     if (!ext.egl.KHR_no_config_context) {
@@ -514,11 +536,16 @@ bool PlatformEGL::isMSAASwapChainSupported(uint32_t samples) const noexcept {
 
     EGLConfig config = EGL_NO_CONFIG_KHR;
     EGLint configsCount;
+    bool supported = false;
     if (!eglChooseConfig(mEGLDisplay, configAttribs.data(), &config, 1, &configsCount)) {
-        return false;
+        supported = false;
+    } else {
+        supported = configsCount > 0;
     }
 
-    return configsCount > 0;
+    mMSAASupport[index] = supported;
+
+    return supported;
 }
 
 Platform::SwapChain* PlatformEGL::createSwapChain(