Glitches after a few dynamic allocations & de-allocation


25-06-2008 03:24:33

I'm using this addon for grass, following the example. It always works perfectly and as expected the first time the instance is dynamically created, i.e. when loading the first mission in my game.

However when deleting the instance and then creating a new one, things go a bit awry. One thing I noticed is that the subsequent instance doesn't work right with respect to min and max range as specified in the call to addDetailLevel<GrassPage>(). For example, the grass squares pop into view rather than fade in, and you notice the "squareness". This is apparent when the min and max ranges have changed for the new instances.

Worse yet, I get no grass at all after the 3rd or 4th iteration of creating a new subsequent instance of PagedGeometry and GrassLoader.

It's as if some static data is involved, and things may not be cleaned up well after deleting the initial instance of PagedGeometry and GrassLoader.

I'll continue digging, but I can't find where the mistake may be mine (at least so far). My code creates and uses these class instances the same way each time, but they don't behave the same way.

Jules Robichaud Gagnon

25-06-2008 23:35:51

Can you recreate the problem with the examples? If you can, send a patch so we can test. :D


26-06-2008 00:39:19

Very good idea, and something I've done in the past. Sometimes you get so wrapped up that you don't see the obvious next step :).


26-06-2008 02:56:41

I'll try to reproduce / debug this problem when I get time, thanks for reporting.

Can you recreate the problem with the examples? If you can, send a patch so we can test. :D
Yeah, recreating problems in the examples is always a huge help :)


28-06-2008 13:07:36

I've recreated the anomaly where grass patches simply appear in chunks. It also doesn't seem to properly use subsequent values for max range.

I tweaked the demo for Example 4 - Grass Loader to demonstrate. It starts at a range of 400. Each time you press 'R' it adds 50 to the range, but if that is over 449, it jumps back to 100. In this case, having a high range in the first instance demonstrates it best. You start at 400 for the first instance, and then back to 100 for the second instance. This shows that the patches instantly appear, and it diesn't look like its properly adhering to the range of 100.

Different issues appear when you have a low range for the first instance, i.e. 100. In that case, subsequent instances don't seem to appear to comply with the greater range.

The other issue I was having with grass not showing is probably my fault. My missions were starting with an uninitialized position for the scene node, resulting in coordinated up near 1E+36. The paged geometry code is unable to recover from this, although doesn't result in any crashes. It's probably not worth the extra guard code to prevent it from blowing up due to absurd coordinates.

Below is Example4.cpp as modified by me.

//Example 4 - GrassLoader
// This example demonstrates the basic use of PagedGeometry to display grass with GrassLoader.
// Instructions: Move around with the arrow/WASD keys, hold SHIFT to move faster, and hold SPACE to fly.
// HINT: Search this source for "[NOTE]" to find important code and comments related to PagedGeometry.
#define AppTitle "PagedGeometry Example 4 - GrassLoader"

//Include windows/Ogre/OIS headers
#include <Ogre.h>
#include <OIS/OIS.h>
#include <windows.h>
using namespace Ogre;

//Include PagedGeometry headers that will be needed
#include "PagedGeometry.h"
#include "GrassLoader.h"

//Include "HeightFunction.h", a header that provides some useful functions for quickly and easily
//getting the height of the terrain at a given point.
#include "HeightFunction.h"
//[NOTE] Remember that this "HeightFunction.h" file is not related to the PagedGeometry library itself
//in any way. It's simply a utility that's included with all these examples to make getting the terrain
//height easy. You can use it in your games/applications if you want, although if you're using a
//collision/physics library with a faster alternate, you may use that instead.

//PagedGeometry's classes and functions are under the "Forests" namespace
using namespace Forests;

//Demo world class
//[NOTE] The main PagedGeometry-related sections of this class are load() and
//render. These functions setup and use PagedGeometry in the scene.
class World

void load(); //Loads the 3D scene
void unload(); //Unloads the 3D scene cleanly
void run(); //Runs the simulation

void render(); //Renders a single frame, updating PagedGeometry and Ogre
void processInput(); //Accepts keyboard and mouse input, allowing you to move around in the world

bool running; //A flag which, when set to false, will terminate a simulation started with run()

//Various pointers to Ogre objects are stored here:
Root *root;
RenderWindow *window;
Viewport *viewport;
SceneManager *sceneMgr;
Camera *camera;

//OIS input objects
OIS::InputManager *inputManager;
OIS::Keyboard *keyboard;
OIS::Mouse *mouse;

//Variables used to keep track of the camera's rotation/etc.
Radian camPitch, camYaw;

//Pointers to PagedGeometry class instances:
PagedGeometry *grass;
GrassLoader *grassLoader;
float maxRange;

INT WINAPI WinMain( HINSTANCE hInst, HINSTANCE hPrevInstance, LPSTR strCmdLine, INT nCmdShow)
int main(int argc, char *argv[])
//By default, Visual Studio sets the working directory to the project folder. This
//sets the working directory to the exe's folder, as it should be.
#ifdef _DEBUG

//Initialize Ogre
Root *root = new Ogre::Root("");

//Load appropriate plugins
//[NOTE] PagedGeometry needs the CgProgramManager plugin to compile shaders
#ifdef _DEBUG
#define STRINGIFY(x) #x
#define EXPAND(x) STRINGIFY(x)
root->loadPlugin(EXPAND(OGRE_PLUGINDIR) "Plugin_CgProgramManager");
root->loadPlugin(EXPAND(OGRE_PLUGINDIR) "Plugin_OctreeSceneManager");
root->loadPlugin(EXPAND(OGRE_PLUGINDIR) "RenderSystem_GL");

//Show Ogre's default config dialog to let the user setup resolution, etc.
bool result = root->showConfigDialog();

//If the user clicks OK, continue
if (result) {
World myWorld;
myWorld.load(); //Load world; //Display world

//Shut down Ogre
delete root;

return 0;

World::World() :
//Setup Ogre::Root and the scene manager
root = Root::getSingletonPtr();
window = root->initialise(true, AppTitle);
sceneMgr = root->createSceneManager(ST_EXTERIOR_CLOSE);

//Initialize the camera and viewport
camera = sceneMgr->createCamera("MainCamera");
viewport = window->addViewport(camera);
viewport->setBackgroundColour(ColourValue(0.47f, 0.67f, 0.96f)); //Blue sky background color
camera->setAspectRatio(Real(viewport->getActualWidth()) / Real(viewport->getActualHeight()));

//Set up lighting
Light *light = sceneMgr->createLight("Sun");
light->setDirection(Vector3(0.0f, -0.5f, 1.0f));
sceneMgr->setAmbientLight(ColourValue(1, 1, 1));

//Load media (trees, grass, etc.)
ResourceGroupManager::getSingleton().addResourceLocation("../../media/trees", "FileSystem");
ResourceGroupManager::getSingleton().addResourceLocation("../../media/terrains", "FileSystem");
ResourceGroupManager::getSingleton().addResourceLocation("../../media/grass", "FileSystem");

//Initialize OIS
using namespace OIS;
size_t windowHnd;
window->getCustomAttribute("WINDOW", &windowHnd);
inputManager = InputManager::createInputSystem(windowHnd);

keyboard = (Keyboard*)inputManager->createInputObject(OISKeyboard, false);
mouse = (Mouse*)inputManager->createInputObject(OISMouse, false);

//Reset camera orientation
camPitch = 0;
camYaw = 0;

//Shut down OIS


//[NOTE] In addition to some Ogre setup, this function configures PagedGeometry in the scene.
void World::load()
//-------------------------------------- LOAD TERRAIN --------------------------------------
//Setup the fog up to 500 units away
sceneMgr->setFog(FOG_LINEAR, viewport->getBackgroundColour(), 0, 100, 700);

//Load the terrain

//Start off with the camera at the center of the terrain
camera->setPosition(700, 100, 700);

//-------------------------------------- LOAD GRASS --------------------------------------
//Create and configure a new PagedGeometry instance for grass
grass = new PagedGeometry(camera, 50);
maxRange += 50.0;
if (maxRange >= 449.0f) { maxRange = 100.0f; }

//Create a GrassLoader object
grassLoader = new GrassLoader(grass);
grass->setPageLoader(grassLoader); //Assign the "treeLoader" to be used to load geometry for the PagedGeometry instance

//Supply a height function to GrassLoader so it can calculate grass Y values

//Add some grass to the scene with GrassLoader::addLayer()
GrassLayer *l = grassLoader->addLayer("grass");

//Configure the grass layer properties (size, density, animation properties, fade settings, etc.)
l->setMinimumSize(2.0f, 2.0f);
l->setMaximumSize(2.5f, 2.5f);
l->setAnimationEnabled(true); //Enable animations
l->setSwayDistribution(10.0f); //Sway fairly unsynchronized
l->setSwayLength(0.5f); //Sway back and forth 0.5 units in length
l->setSwaySpeed(0.5f); //Sway 1/2 a cycle every second
l->setDensity(1.5f); //Relatively dense grass
l->setFadeTechnique(FADETECH_GROW); //Distant grass should slowly raise out of the ground when coming in range
l->setRenderTechnique(GRASSTECH_QUAD); //Draw grass as scattered quads

//This sets a color map to be used when determining the color of each grass quad. setMapBounds()
//is used to set the area which is affected by the color map. Here, "terrain_texture.jpg" is used
//to color the grass to match the terrain under it.
l->setMapBounds(TBounds(0, 0, 1500, 1500)); //(0,0)-(1500,1500) is the full boundaries of the terrain
l->setDensityMap("densitymap.png", CHANNEL_COLOR);

void World::unload()
//[NOTE] Always remember to delete any PageLoader(s) and PagedGeometry instances in order to avoid memory leaks.

//Delete the GrassLoader instance
delete grass->getPageLoader();

//Delete the PagedGeometry instance
delete grass;

void World::run()
//Render loop
running = true;
//Handle windows events

//Update frame

//Exit immediately if the window is closed
if (window->isClosed())

void World::render()
//[NOTE] PagedGeometry::update() is called every frame to keep LODs, etc. up-to-date

//Render the scene with Ogre

void World::processInput()
using namespace OIS;
static Ogre::Timer timer;
static unsigned long lastTime = 0;
unsigned long currentTime = timer.getMilliseconds();

//Calculate the amount of time passed since the last frame
Real timeScale = (currentTime - lastTime) * 0.001f;
if (timeScale < 0.001f)
timeScale = 0.001f;
lastTime = currentTime;

//Get the current state of the keyboard and mouse

//Always exit if ESC is pressed
if (keyboard->isKeyDown(KC_ESCAPE))
running = false;

//Reload the scene if R is pressed
static bool reloadedLast = false;
if (keyboard->isKeyDown(KC_R) && !reloadedLast){
reloadedLast = true;
else {
reloadedLast = false;

//Get mouse movement
const OIS::MouseState &ms = mouse->getMouseState();

//Update camera rotation based on the mouse
camYaw += Radian(-ms.X.rel / 200.0f);
camPitch += Radian(-ms.Y.rel / 200.0f);

//Allow the camera to move around with the arrow/WASD keys
Ogre::Vector3 trans(0, 0, 0);
if (keyboard->isKeyDown(KC_UP) || keyboard->isKeyDown(KC_W))
trans.z = -1;
if (keyboard->isKeyDown(KC_DOWN) || keyboard->isKeyDown(KC_S))
trans.z = 1;
if (keyboard->isKeyDown(KC_RIGHT) || keyboard->isKeyDown(KC_D))
trans.x = 1;
if (keyboard->isKeyDown(KC_LEFT) || keyboard->isKeyDown(KC_A))
trans.x = -1;
if (keyboard->isKeyDown(KC_PGUP) || keyboard->isKeyDown(KC_E))
trans.y = 1;
if (keyboard->isKeyDown(KC_PGDOWN) || keyboard->isKeyDown(KC_Q))
trans.y = -1;

//Shift = speed boost
if (keyboard->isKeyDown(KC_LSHIFT) || keyboard->isKeyDown(KC_RSHIFT))
trans *= 2;

trans *= 50;
camera->moveRelative(trans * timeScale);

//Make sure the camera doesn't go under the terrain
Ogre::Vector3 camPos = camera->getPosition();
float terrY = HeightFunction::getTerrainHeight(camPos.x, camPos.z);
if (camPos.y < terrY + 3 || !keyboard->isKeyDown(KC_SPACE)){ //Space = fly
camPos.y = terrY + 3;


01-07-2008 16:13:17

Thanks for the code, that really helped. The problem should be fixed now in the latest version (SVN).

The issue was much easier to fix than I thought - the internal shader ID string simply needed the fade range added so it can distinguish changes in this value (and update them).

Sorry I didn't fix this earlier - I was away during the weekend.