History: Rectangle2D as Player GUI Feedback for Game
Preview of version: 2
So this explains how to use GUI for player feedback in your game, such as showing blood onscreen when the player gets hit.
This specific example uses alpha to fade the image onto and off the screen.
Here's an animated GIF to show the idea:
Here is my simple material script:
material Blood { technique { pass { lighting on ambient 1 1 1 diffuse 1 1 1 emissive 0 0 0 1 alpha_rejection greater 128 texture_unit { texture blood.png scale 1 1 } } } }
Some variables to set this up, I put these in my class Player.
// Node for onscreen blood Ogre::SceneNode *BloodNode; // Rectangle containing blood material Ogre::Rectangle2D *BloodScreen; // Boolean used to enable showing of blood bool showBlood; // Length blood will be shown onscreen Ogre::Real bloodTime; // Used to change alpha of bloodscren int bloodAlpha; // Boolean on whether alpha should increase/decrease bool bloodUp; // Functions to start and display blood onscreen void startBlood() void displayBlood();
Now initialize everything
int ScreenX = APP->Viewport->getActualHeight(); int ScreenY = APP->Viewport->getActualWidth(); double XRatio = ScreenX/1600.0; double YRatio = ScreenY/900.0; BloodScreen = new Ogre::Rectangle2D(true); BloodScreen->setCorners(-2.08*XRatio,YRatio/1.5,2.08*XRatio,-1*YRatio/1.5); BloodScreen->setMaterial("Blood"); BloodScreen->setRenderQueueGroup(Ogre::RENDER_QUEUE_BACKGROUND); Ogre::AxisAlignedBox box; box.setInfinite(); BloodScreen->setBoundingBox(box); BloodNode = SceneMgr->getRootSceneNode()->createChildSceneNode("BloodScreen"); BloodNode->attachObject(BloodScreen); BloodNode->setVisible(false); bloodCount = 255; bloodUp = false; showBlood = false;
Next we need to start showing the onscreen feedback during a certain action.
Do this in frameRenderingQueued
void Player::frameRenderingQueued(const Ogre::FrameEvent &evt) { if (PlayerAction & PLAYER_HIT) { disableAction(PLAYER_HIT); startBlood(); } if (showBlood) displayBlood(); }
Next is the startBlood() function, this starts the process of course.
void Player::startBlood() { // Display blood node BloodNode->setVisible(true); showBlood = true; // Get how much time has passed since program started and add how much time to show blood bloodTime = APP->getCurrentFrame() + 5000; bloodCount = 255; }
And now the meat of it, fading the blood onto the screen and back off.
void Player::displayBlood(const Ogre::FrameEvent &evt) { // Check if enough time has passed // i.e. the current time is greater than how much time we needed if (bloodTime < APP->getCurrentFrame()) { showBlood = false; BloodNode->setVisible(false); return; } // If current alpha is at 0, increase alpha otherwise decrease it if (bloodCount <= 0) bloodUp = true; else if (bloodCount >= 255) bloodUp = false; if (bloodUp) bloodCount++; else bloodCount--; // Get material in order to apply alpha Ogre::MaterialPtr mat = BloodScreen->getMaterial(); // Apply alpha value mat->getTechnique(0)->getPass(0)->setAlphaRejectValue((unsigned char)bloodCount); }
And there you have it! You may want to pass in either (const Ogre::FrameEvent &evt) or (evt.timeSinceLastFrame) to displayBlood()
and calculate the alpha change according to evt.timeSinceLastFrame to account for jumps in FPS.
And you will need to adjust the time (I put 4000) to how much time you need; and of course if you don't want the fade in/out and just
want it to go on screen then omit the alpha change and simply set the node's visibility to off when the time is up.
Hope you enjoy it.