adapter: snapshots fall back to a quad/cylinder layer and log brightness

Frames without a projection layer (e.g. PreyVR's menu, a cylinder layer only) gave no snapshot. The snapshot now
takes the first quad/cylinder layer's image instead and logs the layer type, image area, array index and the mean/max
brightness of the submitted area, so a black image shows in the log without fetching the file (#306).

artifacts/SHA256SUMS

@@ -13,11 +13,11 @@ e8c0965c188665a4e565e4a3af983ef1866d1cf9225665cc90d8df286bc96ef3  ./arm64-v8a/li
 5432674a59d02f411cd853a5dc57e3fa547d1ac518f25bf433fc54c43677177a  ./arm64-v8a/libfpglmv.so
 8a8f6b1da8952cb3933a5b53558424a5fc56043b2527a16bb6dd62a00d2de01a  ./arm64-v8a/libframe_xrshim.so
 19ba5ed3c4b780f5ae46251f6958f552acfc5f13c8bb39f995579593fa8990c6  ./arm64-v8a/libglshim.so
-0f058921e9c1f5b9ef5847cc9e6b80a23e75028c76c1d3bb02d1610b535f81c9  ./arm64-v8a/libopenxr_loader_generic.so
+82cc4e8fd3d7457ad2af3f0f756876661bfd4b4c5199c70bd219a192d67cb356  ./arm64-v8a/libopenxr_loader_generic.so
 1feaeafad467c4cafdf2b018a4d84b0bee200c3f711697b4ce97e66a3ba256ca  ./arm64-v8a/libovrplatformcompat.so
 a4ed80ae45ca90758239f152ea5a2e8c127d491e1e697ea5680db6fd7f72db07  ./arm64-v8a/libvrapi.so
 a4ed80ae45ca90758239f152ea5a2e8c127d491e1e697ea5680db6fd7f72db07  ./arm64-v8a/libvrapi_foveation.so
-9e8a7ce599b62a7c607b0d3637e4ec1b1ea1974c3373a7af3f5920ad2adc5e00  ./armeabi-v7a/libopenxr_loader_generic.so
+9b5924356fbe93d7660833fae59f1e7eb88797dc8830d5c619b2c403811b31d9  ./armeabi-v7a/libopenxr_loader_generic.so
 1871eae093432d277da4bc751bf5f3269dfcf11f9168260b0c3caadb0dedb19d  ./dex/oculusos-stubs.dex
 b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe  ./hevc/COPYING.FFmpeg
 141de01f0d40b97d4f9a720db5ab8ea442f6aa35db5272048899292884994a1c  ./hevc/libstagefrighthw.so

native/adapter/snapshot_gl.c

@@ -1,6 +1,6 @@
 // FramePort FrameBridge: eye-image snapshots for headless diagnostics (setting snapshot=<seconds>, GLES games only).
 // Every <seconds>, at xrEndFrame, the left-eye image the game just submitted (projection layer, view 0: its swapchain
-// image and array layer) is read back on the game's own GL context and written at a quarter of its size as
+// image and array layer; without a projection layer the first quad/cylinder layer's) is read back on the game's own GL context and written at a quarter of its size as
 // /sdcard/Android/data/<package>/files/fb_snap_<n>.ppm (n = 0-7, the oldest is overwritten). Nobody wears the headset
 // in a launch test, so the headset view stays black: this shows what the game itself draws (e.g. which screen it is
 // stuck on). The game's framebuffer, pack-buffer and pack-alignment bindings are restored afterwards.
@@ -118,18 +118,27 @@ static void snap_end_frame(const XrFrameEndInfo *info) {
     int64_t t = (int64_t)now.tv_sec * 1000000000ll + now.tv_nsec;
     if (t < next_ns) return;
     next_ns = t + (int64_t)snapshot * 1000000000ll;
-    const XrCompositionLayerProjection *proj = NULL;
-    for (uint32_t i = 0; i < info->layerCount && !proj; ++i)
+    // The projection layer's left eye; a frame without one (e.g. a menu shown only as a quad or cylinder layer) gives
+    // its first quad/cylinder layer's image instead.
+    const XrSwapchainSubImage *sub = NULL;
+    int type = 0;
+    for (uint32_t i = 0; i < info->layerCount && !sub; ++i)
         if (info->layers[i] && info->layers[i]->type == XR_TYPE_COMPOSITION_LAYER_PROJECTION &&
             ((const XrCompositionLayerProjection *)info->layers[i])->viewCount)
-            proj = (const XrCompositionLayerProjection *)info->layers[i];
-    if (!proj || !snap_load_gl()) return;
+            sub = &((const XrCompositionLayerProjection *)info->layers[i])->views[0].subImage, type = info->layers[i]->type;
+    for (uint32_t i = 0; i < info->layerCount && !sub; ++i) {
+        const XrCompositionLayerBaseHeader *layer = info->layers[i];
+        if (layer && layer->type == XR_TYPE_COMPOSITION_LAYER_QUAD)
+            sub = &((const XrCompositionLayerQuad *)layer)->subImage, type = layer->type;
+        else if (layer && layer->type == XR_TYPE_COMPOSITION_LAYER_CYLINDER_KHR)
+            sub = &((const XrCompositionLayerCylinderKHR *)layer)->subImage, type = layer->type;
+    }
+    if (!sub || !snap_load_gl()) return;
     if (!s_eglGetCurrentContext()) {
         static int logged;
         if (!logged++) LOG("snapshot: no GL context current in xrEndFrame, no snapshot");
         return;
     }
-    const XrSwapchainSubImage *sub = &proj->views[0].subImage;
     pthread_mutex_lock(&snap_lock);
     int i = snap_find(sub->swapchain, 0);
     GLuint tex = 0;
@@ -167,6 +176,21 @@ static void snap_end_frame(const XrFrameEndInfo *info) {
     s_glDeleteFramebuffers(1, &fb);
     while (s_glGetError() != GL_NO_ERROR) {}  // our calls must not leave errors for the game to find
     if (rgba) {
+        // brightness of the submitted area: tells a black image from a drawn one without fetching the file
+        uint64_t sum = 0, n = 0;
+        unsigned max = 0;
+        const XrRect2Di *r = &sub->imageRect;
+        for (int32_t y = r->offset.y; y < r->offset.y + r->extent.height; y += 4)
+            for (int32_t x = r->offset.x; x < r->offset.x + r->extent.width; x += 4) {
+                if (x < 0 || y < 0 || (uint32_t)x >= w || (uint32_t)y >= h) continue;
+                const unsigned char *p = rgba + ((size_t)y * w + (size_t)x) * 4;
+                unsigned v = p[0] > p[1] ? (p[0] > p[2] ? p[0] : p[2]) : (p[1] > p[2] ? p[1] : p[2]);
+                sum += v, ++n;
+                if (v > max) max = v;
+            }
+        LOG("snapshot: layer type=%d image %u array=%u rect=%d,%d %dx%d of %ux%u: mean %.1f max %u",
+            type, tex, sub->imageArrayIndex, r->offset.x, r->offset.y, r->extent.width, r->extent.height, w, h,
+            n ? (double)sum / (double)n : 0.0, max);
         snap_write(rgba, w, h, taken++ % 8);
         free(rgba);
     }