Tutorial 6: 2D Graphics

This Tutorial shows how to do 2d graphics with the Irrlicht Engine. It shows how to draw images, keycolor based sprites, transparent rectangles, and different fonts. You may consider this useful if you want to make a 2d game with the engine, or if you want to draw a cool interface or head up display for your 3d game.

As always, I include the header files, use the irr namespace, and tell the linker to link with the .lib file.

#include <irrlicht.h>
#include "driverChoice.h"
using namespace irr;
#ifdef _MSC_VER
#pragma comment(lib, "Irrlicht.lib")
#endif

At first, we let the user select the driver type, then start up the engine, set a caption, and get a pointer to the video driver.

int main()
{
// ask user for driver
video::E_DRIVER_TYPE driverType=driverChoiceConsole();
if (driverType==video::EDT_COUNT)
return 1;
// create device
IrrlichtDevice *device = createDevice(driverType,
core::dimension2d<u32>(512, 384));
if (device == 0)
return 1; // could not create selected driver.
device->setWindowCaption(L"Irrlicht Engine - 2D Graphics Demo");
video::IVideoDriver* driver = device->getVideoDriver();

All 2d graphics in this example are put together into one texture, 2ddemo.png. Because we want to draw colorkey based sprites, we need to load this texture and tell the engine, which part of it should be transparent based on a colorkey.

In this example, we don't tell it the color directly, we just say "Hey Irrlicht Engine, you'll find the color I want at position (0,0) on the texture.". Instead, it would be also possible to call driver->makeColorKeyTexture(images, video::SColor(0,0,0,0)), to make e.g. all black pixels transparent. Please note that makeColorKeyTexture just creates an alpha channel based on the color.

video::ITexture* images = driver->getTexture("../../media/2ddemo.png");
driver->makeColorKeyTexture(images, core::position2d<s32>(0,0));

To be able to draw some text with two different fonts, we first load them. Ok, we load just one. As the first font we just use the default font which is built into the engine. Also, we define two rectangles which specify the position of the images of the red imps (little flying creatures) in the texture.

gui::IGUIFont* font = device->getGUIEnvironment()->getBuiltInFont();
gui::IGUIFont* font2 =
device->getGUIEnvironment()->getFont("../../media/fonthaettenschweiler.bmp");
core::rect<s32> imp1(349,15,385,78);
core::rect<s32> imp2(387,15,423,78);

Prepare a nicely filtering 2d render mode for special cases.

driver->getMaterial2D().TextureLayer[0].BilinearFilter=true;
driver->getMaterial2D().AntiAliasing=video::EAAM_FULL_BASIC;

Everything is prepared, now we can draw everything in the draw loop, between the begin scene and end scene calls. In this example, we are just doing 2d graphics, but it would be no problem to mix them with 3d graphics. Just try it out, and draw some 3d vertices or set up a scene with the scene manager and draw it.

while(device->run() && driver)
{
if (device->isWindowActive())
{
u32 time = device->getTimer()->getTime();
driver->beginScene(true, true, video::SColor(255,120,102,136));

First, we draw 3 sprites, using the alpha channel we created with makeColorKeyTexture. The last parameter specifies that the drawing method should use this alpha channel. The last-but-one parameter specifies a color, with which the sprite should be colored. (255,255,255,255) is full white, so the sprite will look like the original. The third sprite is drawn with the red channel modulated based on the time.

// draw fire & dragons background world
driver->draw2DImage(images, core::position2d<s32>(50,50),
core::rect<s32>(0,0,342,224), 0,
video::SColor(255,255,255,255), true);
// draw flying imp
driver->draw2DImage(images, core::position2d<s32>(164,125),
(time/500 % 2) ? imp1 : imp2, 0,
video::SColor(255,255,255,255), true);
// draw second flying imp with colorcylce
driver->draw2DImage(images, core::position2d<s32>(270,105),
(time/500 % 2) ? imp1 : imp2, 0,
video::SColor(255,(time) % 255,255,255), true);

Drawing text is really simple. The code should be self explanatory.

// draw some text
if (font)
font->draw(L"This demo shows that Irrlicht is also capable of drawing 2D graphics.",
core::rect<s32>(130,10,300,50),
video::SColor(255,255,255,255));
// draw some other text
if (font2)
font2->draw(L"Also mixing with 3d graphics is possible.",
core::rect<s32>(130,20,300,60),
video::SColor(255,time % 255,time % 255,255));

Next, we draw the Irrlicht Engine logo (without using a color or an alpha channel). Since we slightly scale the image we use the prepared filter mode.

driver->enableMaterial2D();
driver->draw2DImage(images, core::rect<s32>(10,10,108,48),
core::rect<s32>(354,87,442,118));
driver->enableMaterial2D(false);

Finally draw a half-transparent rect under the mouse cursor.

core::position2d<s32> m = device->getCursorControl()->getPosition();
driver->draw2DRectangle(video::SColor(100,255,255,255),
core::rect<s32>(m.X-20, m.Y-20, m.X+20, m.Y+20));
driver->endScene();
}
}
device->drop();
return 0;
}

That's all. I hope it was not too difficult.