Fix the stack overflow when drawing a long polyline

CHANGELOG.md

@@ -100,6 +100,7 @@
 - **iOS downloads from a signed URL are saved (`VROPlatformDownloadURLToFile`, `VROPlatformDownloadURLToFileAsync`).** The temporary file was named after the URL's last path component with its query, and a signed URL's token pushed the name past the 255-byte file name limit, so the write failed and the download still reported success with a file that did not exist. `VROPlatformLastPathComponent` drops the query and fragment, and a failed write now fails the download.
 - **Android: a camera added before the renderer no longer crashes (`VROPlatformUtil`, #597).** `libviro_renderer.so` now sets the `JavaVM` in `JNI_OnLoad`. It was set only when a renderer or loader started, and under Fabric `ViroARCamera`'s view is built first, so adding its node reached `getJNIEnv` with no VM.
 - **A GLB whose skins share joints animates every skin (`VROGLTFLoader`, #599).** Resampling runs once per skin and rewrote a shared joint's channels in place; the next skin's pass kept only the translation of the merged channel, so those joints lost their rotation and scale. Every property of a channel is now copied.
+- **A long polyline no longer overflows the stack (`VROPolyline`, `VROPolygon`).** `buildElement` built its index list as a variable-length array on the stack. The world mesh's debug drawing (`debugDrawEnabled`) on an accumulated mesh reaches hundreds of thousands of line corners, which overflowed the iOS main thread's stack and crashed the app. The list is on the heap now, as is a polygon's.
 
 ### Removed
 

ViroRenderer/VROPolygon.cpp

@@ -24,6 +24,7 @@
 //  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #include "VROPolygon.h"
+#include <vector>
 #include "VROData.h"
 #include "VROGeometryUtil.h"
 #include "VROGeometrySource.h"
@@ -189,12 +190,13 @@ void VROPolygon::buildGeometry(std::vector<std::shared_ptr<VROGeometrySource>> &
 }
 
 std::shared_ptr<VROGeometryElement> VROPolygon::buildElement(size_t numCorners) {
-    int indices[numCorners];
-    for (int i = 0; i < numCorners; i++) {
-        indices[i] = i;
+    // On the heap: the corner count has no bound, so a stack array could overflow.
+    std::vector<int> indices(numCorners);
+    for (size_t i = 0; i < numCorners; i++) {
+        indices[i] = (int) i;
     }
 
-    std::shared_ptr<VROData> indexData = std::make_shared<VROData>((void *) indices, sizeof(int) * numCorners);
+    std::shared_ptr<VROData> indexData = std::make_shared<VROData>((void *) indices.data(), sizeof(int) * numCorners);
     std::shared_ptr<VROGeometryElement> element= std::make_shared<VROGeometryElement>(indexData,
                                                                                       VROGeometryPrimitiveType::Triangle,
                                                                                       VROGeometryUtilGetPrimitiveCount((int) numCorners,

ViroRenderer/VROPolyline.cpp

@@ -24,6 +24,7 @@
 //  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 //  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+#include <vector>
 #include "VROPolyline.h"
 #include "VROLog.h"
 #include "VROByteBuffer.h"
@@ -211,12 +212,14 @@ void VROPolyline::buildGeometry(std::vector<std::vector<VROVector3f>> &paths,
 }
 
 std::shared_ptr<VROGeometryElement> VROPolyline::buildElement(size_t numCorners) {
-    int indices[numCorners];
-    for (int i = 0; i < numCorners; i++) {
-        indices[i] = i;
+    // On the heap: a world mesh's debug lines reach hundreds of thousands of corners,
+    // which overflowed the render thread's stack as a variable-length array.
+    std::vector<int> indices(numCorners);
+    for (size_t i = 0; i < numCorners; i++) {
+        indices[i] = (int) i;
     }
 
-    std::shared_ptr<VROData> indexData = std::make_shared<VROData>((void *) indices, sizeof(int) * numCorners);
+    std::shared_ptr<VROData> indexData = std::make_shared<VROData>((void *) indices.data(), sizeof(int) * numCorners);
     std::shared_ptr<VROGeometryElement> element = std::make_shared<VROGeometryElement>(indexData,
                                                                                        VROGeometryPrimitiveType::TriangleStrip,
                                                                                        VROGeometryUtilGetPrimitiveCount((int) numCorners, VROGeometryPrimitiveType::TriangleStrip),