Basic Pan/Zoom extension for olc::PixelGameEngine. Adapted from javidx9's panning & zooming tutorial.
To begin with you'll want to declare an olc::panzoom somewhere accessible in your application. A private member variable of your derived PGE class is suitable.
class MyApp : public olc::PixelGameEngine
{
private:
olc::panzoom pz;
};The extension requires a pointer to your derived PGE class. You can provide it with one within your OnUserCreate method. You can also optionally set the offset with an olc::vf2d here. To emulate a euclidean plane with (0,0) at the center, you can set the offset to (-ScreenWidth() / 2, -ScreenHeight() / 2):
bool OnUserCreate() override
{
pz.Create(this);
pz.SetOffset({ (float)-ScreenWidth() * 0.5f, (float)-ScreenHeight() * 0.5f });
}Input handling is left to the user and instead several methods are presented: StartPan, StopPan, ZoomIn, ZoomOut, NudgeLeft, NudgeRight, NudgeUp, NudgeDown. The extension also provides an Update method which must be called once per frame in order to process panning. NOTE: the Nudge methods nudge the 'Camera', not the world.
The following basic example implements panning with the middle mouse button, and zooming with the mouse wheel:
bool OnUserUpdate(float fElapsedTime)
{
if (GetMouse(2).bPressed)
pz.StartPan();
if (GetMouse(2).bReleased)
pz.StopPan();
if (GetMouseWheel() > 0)
pz.ZoomIn(1.1f);
if (GetMouseWheel() < 0)
pz.ZoomOut(0.9f);
// call the panzoom Update method or panning won't work
pz.Update(fElapsedTime);
}The ZoomIn and ZoomOut methods have an optional float fScaleFactor argument should you wish to have finer control over the speed of the zoom. Depending on whether keyboard or mousewheel zoom is used you may want to adjust these - the mousewheel moves in discrete steps and requires a larger 'jump'; occurring in a single frame as opposed to keyboard zoom will also effect this.
if (GetKey(olc::Q).bHeld)
pz.ZoomIn(1.01f);
if (GetMouseWheel() > 0)
pz.ZoomIn(1.1f);
if (GetKey(olc::A).bHeld)
pz.ZoomOut(0.99f);
if (GetMouseWheel() < 0)
pz.ZoomOut(0.9f);By default, zooming will occur around the mouse cursor. If you'd prefer to disable this and instead zoom around the screen center, there is a second optional bool zoomToMouse argument for the ZoomIn and ZoomOut methods.
// keyboard zoom on center (not mouse)
if (GetKey(olc::Q).bHeld)
pz.ZoomIn(1.01f, false);
if (GetKey(olc::A).bHeld)
pz.ZoomOut(0.99f, false);None of this is of any use unless we use it to transform co-ordinates between world-space and screen-space. This can be performed with the ScreenToWorld and WorldToScreen methods. The following example converts the top-left and bottom-right of the screen into co-ordinates in world space, and plots the function y = x - taking the values from world space and drawing them in screen space.
olc::vf2d wldTopLeft, wldBottomRight;
pz.ScreenToWorld({ 0, 0 }, wldTopLeft);
pz.ScreenToWorld({ ScreenWidth(), ScreenHeight() }, wldBottomRight);
olc::vi2d previousPos; // used to draw lines between co-ordinates
for (float x = wldTopLeft.x; x < wldBottomRight.x; x++)
{
float y = x; // perform the basic function y = x
olc::vi2d scrPos; // declare an olc::vi2d to hold our screen pos
pz.WorldToScreen({ x, y }, scrPos); // convert from world to screen space
if (x != wldTopLeft.x) // if not the first iteration of this loop:
DrawLine(previousPos, scrPos); // draw a line between previousPos and current scrPos
previousPos = scrPos; // update previousPos with current scrPos
}There are instances where you may also want to scale a scalar value based on the zoom factor of the panzoom instance - such as calculating the screen-space radius of a circle.
olc::vi2d scrCirclePos;
int scrRadius;
pz.WorldToScreen({ 0.0f, 0.0f }, scrCirclePos); // center of circle at origin (0,0) from world space to screen
scrRadius = pz.ToScreenScale(30.0f); // scale radius of 30.0f in world space to screen-space
DrawCircle(scrCirclePos, scrRadius);
DrawLine(scrCirclePos, { scrCirclePos.x + scrRadius, scrCirclePos.y });
// and to calculate value at world scale
float wldRadius = pz.ToWorldScale(scrRadius); // should be close to 30.0f depending on current zoom factorPlease see the example.cpp file for a full working demo. Don't forget to #define OLC_PGEX_PANZOOM alongside OLC_PGE_APPLICATION.
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