I found a code snippet here for a strategy game camera control system that was designed by Ninth. The code he wrote was really excellent and effective, but I found I needed something a bit more robust for my own purposes and I started modifying it. In the spirit of giving back to the community, I decided to share those modifications.
The basic idea behind the camera control is this: When the user moves the mouse cursor to the edge of the screen, the camera pans in that direction. When the user holds the right mouse button, moving the mouse will rotate the camera such that it orbits around it’s target point while still looking at said target. The mouse wheel will move the camera closer to or further from it’s target point.
Here’s the list of changes I made, which can also be found in comments in the actual code:
# First mod: Comments. I've gone through the code and added comments to explain what is doing what, and the reason for each line of code.
# Second mod: Name changes. I changed some names of variables and functions to make the code a bit more readable (in my opinion).
# Third mod: Variable pan rate. I have changed the camera panning when the mouse is moved to the edge of the screen so that the panning rate is dependant on the distance the camera has been zoomed out. This prevents the panning from appearing faster when zoomed in than when zoomed out. I have also added a pan rate variable, which could be modified by an options menu, so it is easier to give the player control over how fast the camera pans.
# Fourth mod: Variable pan zones. I added a variable to control the size of the zones at the edge of the screen where the camera starts panning.
# Fifth mod: Orbit limits: I put in a system to limit how far the camera can move along it's Y orbit to prevent it from moving below the ground plane or so high that you get a fast rotation glitch.
# Sixth mod: Pan limits: I put in variables to use for limiting how far the camera can pan, so the camera can't pan away from the map. These values will need to be customized to the map, so I added a function for setting them.
Most of the math used in this code is a bit over my head, so I wasn’t able to properly explain it in the comments. If anyone wants to fix that problem, that would be stellar.
from direct.showbase import DirectObject
from pandac.PandaModules import Vec3,Vec2
import math
# Last modified: 10/2/2009
# This class takes over control of the camera and sets up a Real Time Strategy game type camera control system. The user can move the camera three
# ways. If the mouse cursor is moved to the edge of the screen, the camera will pan in that direction. If the right mouse button is held down, the
# camera will orbit around it's target point in accordance with the mouse movement, maintaining a fixed distance. The mouse wheel will move the
# camera closer to or further from it's target point.
# This code was originally developed by Ninth from the Panda3D forums, and has been modified by piratePanda to achieve a few effects.
# First mod: Comments. I've gone through the code and added comments to explain what is doing what, and the reason for each line of code.
# Second mod: Name changes. I changed some names of variables and functions to make the code a bit more readable (in my opinion).
# Third mod: Variable pan rate. I have changed the camera panning when the mouse is moved to the edge of the screen so that the panning
# rate is dependant on the distance the camera has been zoomed out. This prevents the panning from appearing faster when
# zoomed in than when zoomed out. I have also added a pan rate variable, which could be modified by an options menu, so it is
# easier to give the player control over how fast the camera pans.
# Fourth mod: Variable pan zones. I added a variable to control the size of the zones at the edge of the screen where the camera starts
# panning.
# Fifth mod: Orbit limits: I put in a system to limit how far the camera can move along it's Y orbit to prevent it from moving below the ground
# plane or so high that you get a fast rotation glitch.
# Sixth mod: Pan limits: I put in variables to use for limiting how far the camera can pan, so the camera can't pan away from the map. These
# values will need to be customized to the map, so I added a function for setting them.
class CameraHandler(DirectObject.DirectObject):
def __init__(self):
base.disableMouse()
# This disables the default mouse based camera control used by panda. This default control is awkward, and won't be used.
base.camera.setPos(0,20,20)
base.camera.lookAt(0,0,0)
# Gives the camera an initial position and rotation.
self.mx,self.my=0,0
# Sets up variables for storing the mouse coordinates
self.orbiting=False
# A boolean variable for specifying whether the camera is in orbiting mode. Orbiting mode refers to when the camera is being moved
# because the user is holding down the right mouse button.
self.target=Vec3()
# sets up a vector variable for the camera's target. The target will be the coordinates that the camera is currently focusing on.
self.camDist = 40
# A variable that will determine how far the camera is from it's target focus
self.panRateDivisor = 20
# This variable is used as a divisor when calculating how far to move the camera when panning. Higher numbers will yield slower panning
# and lower numbers will yield faster panning. This must not be set to 0.
self.panZoneSize = .15
# This variable controls how close the mouse cursor needs to be to the edge of the screen to start panning the camera. It must be less than 1,
# and I recommend keeping it less than .2
self.panLimitsX = Vec2(-20, 20)
self.panLimitsY = Vec2(-20, 20)
# These two vairables will serve as limits for how far the camera can pan, so you don't scroll away from the map.
self.setTarget(0,0,0)
# calls the setTarget function to set the current target position to the origin.
self.turnCameraAroundPoint(0,0)
# calls the turnCameraAroundPoint function with a turn amount of 0 to set the camera position based on the target and camera distance
self.accept("mouse3",self.startOrbit)
# sets up the camrea handler to accept a right mouse click and start the "drag" mode.
self.accept("mouse3-up",self.stopOrbit)
# sets up the camrea handler to understand when the right mouse button has been released, and ends the "drag" mode when
# the release is detected.
# The next pair of lines use lambda, which creates an on-the-spot one-shot function.
self.accept("wheel_up",lambda : self.adjustCamDist(0.9))
# sets up the camera handler to detet when the mouse wheel is rolled upwards and uses a lambda function to call the
# adjustCamDist function with the argument 0.9
self.accept("wheel_down",lambda : self.adjustCamDist(1.1))
# sets up the camera handler to detet when the mouse wheel is rolled upwards and uses a lambda function to call the
# adjustCamDist function with the argument 1.1
taskMgr.add(self.camMoveTask,'camMoveTask')
# sets the camMoveTask to be run every frame
def turnCameraAroundPoint(self,deltaX,deltaY):
# This function performs two important tasks. First, it is used for the camera orbital movement that occurs when the
# right mouse button is held down. It is also called with 0s for the rotation inputs to reposition the camera during the
# panning and zooming movements.
# The delta inputs represent the change in rotation of the camera, which is also used to determine how far the camera
# actually moves along the orbit.
newCamHpr = Vec3()
newCamPos = Vec3()
# Creates temporary containers for the new rotation and position values of the camera.
camHpr=base.camera.getHpr()
# Creates a container for the current HPR of the camera and stores those values.
newCamHpr.setX(camHpr.getX()+deltaX)
newCamHpr.setY(self.clamp(camHpr.getY()-deltaY, -85, -10))
newCamHpr.setZ(camHpr.getZ())
# Adjusts the newCamHpr values according to the inputs given to the function. The Y value is clamped to prevent
# the camera from orbiting beneath the ground plane and to prevent it from reaching the apex of the orbit, which
# can cause a disturbing fast-rotation glitch.
base.camera.setHpr(newCamHpr)
# Sets the camera's rotation to the new values.
angleradiansX = newCamHpr.getX() * (math.pi / 180.0)
angleradiansY = newCamHpr.getY() * (math.pi / 180.0)
# Generates values to be used in the math that will calculate the new position of the camera.
newCamPos.setX(self.camDist*math.sin(angleradiansX)*math.cos(angleradiansY)+self.target.getX())
newCamPos.setY(-self.camDist*math.cos(angleradiansX)*math.cos(angleradiansY)+self.target.getY())
newCamPos.setZ(-self.camDist*math.sin(angleradiansY)+self.target.getZ())
base.camera.setPos(newCamPos.getX(),newCamPos.getY(),newCamPos.getZ())
# Performs the actual math to calculate the camera's new position and sets the camera to that position.
#Unfortunately, this math is over my head, so I can't fully explain it.
base.camera.lookAt(self.target.getX(),self.target.getY(),self.target.getZ() )
# Points the camera at the target location.
def setTarget(self,x,y,z):
#This function is used to give the camera a new target position.
x = self.clamp(x, self.panLimitsX.getX(), self.panLimitsX.getY())
self.target.setX(x)
y = self.clamp(y, self.panLimitsY.getX(), self.panLimitsY.getY())
self.target.setY(y)
self.target.setZ(z)
# Stores the new target position values in the target variable. The x and y values are clamped to the pan limits.
def setPanLimits(self,xMin, xMax, yMin, yMax):
# This function is used to set the limitations of the panning movement.
self.panLimitsX = (xMin, xMax)
self.panLimitsY = (yMin, yMax)
# Sets the inputs into the limit variables.
def clamp(self, val, minVal, maxVal):
# This function constrains a value such that it is always within or equal to the minimum and maximum bounds.
val = min( max(val, minVal), maxVal)
# This line first finds the larger of the val or the minVal, and then compares that to the maxVal, taking the smaller. This ensures
# that the result you get will be the maxVal if val is higher than it, the minVal if val is lower than it, or the val itself if it's
# between the two.
return val
# returns the clamped value
def startOrbit(self):
# This function puts the camera into orbiting mode.
self.orbiting=True
# Sets the orbiting variable to true to designate orbiting mode as on.
def stopOrbit(self):
# This function takes the camera out of orbiting mode.
self.orbiting=False
# Sets the orbiting variable to false to designate orbiting mode as off.
def adjustCamDist(self,distFactor):
# This function increases or decreases the distance between the camera and the target position to simulate zooming in and out.
# The distFactor input controls the amount of camera movement.
# For example, inputing 0.9 will set the camera to 90% of it's previous distance.
self.camDist=self.camDist*distFactor
# Sets the new distance into self.camDist.
self.turnCameraAroundPoint(0,0)
# Calls turnCameraAroundPoint with 0s for the rotation to reset the camera to the new position.
def camMoveTask(self,task):
# This task is the camera handler's work house. It's set to be called every frame and will control both orbiting and panning the camera.
if base.mouseWatcherNode.hasMouse():
# We're going to use the mouse, so we have to make sure it's in the game window. If it's not and we try to use it, we'll get
# a crash error.
mpos = base.mouseWatcherNode.getMouse()
# Gets the mouse position
if self.orbiting:
# Checks to see if the camera is in orbiting mode. Orbiting mode overrides panning, because it would be problematic if, while
# orbiting the camera the mouse came close to the screen edge and started panning the camera at the same time.
self.turnCameraAroundPoint((self.mx-mpos.getX())*100,(self.my-mpos.getY())*100)
# calculates new values for camera rotation based on the change in mouse position. mx and my are used here as the old
# mouse position.
else:
# If the camera isn't in orbiting mode, we check to see if the mouse is close enough to the edge of the screen to start panning
moveY=False
moveX=False
# these two booleans are used to denote if the camera needs to pan. X and Y refer to the mouse position that causes the
# panning. X is the left or right edge of the screen, Y is the top or bottom.
if self.my > (1 - self.panZoneSize):
angleradiansX1 = base.camera.getH() * (math.pi / 180.0)
panRate1 = (1 - self.my - self.panZoneSize) * (self.camDist / self.panRateDivisor)
moveY = True
if self.my < (-1 + self.panZoneSize):
angleradiansX1 = base.camera.getH() * (math.pi / 180.0)+math.pi
panRate1 = (1 + self.my - self.panZoneSize)*(self.camDist / self.panRateDivisor)
moveY = True
if self.mx > (1 - self.panZoneSize):
angleradiansX2 = base.camera.getH() * (math.pi / 180.0)+math.pi*0.5
panRate2 = (1 - self.mx - self.panZoneSize) * (self.camDist / self.panRateDivisor)
moveX = True
if self.mx < (-1 + self.panZoneSize):
angleradiansX2 = base.camera.getH() * (math.pi / 180.0)-math.pi*0.5
panRate2 = (1 + self.mx - self.panZoneSize) * (self.camDist / self.panRateDivisor)
moveX = True
# These four blocks check to see if the mouse cursor is close enough to the edge of the screen to start panning and then
# perform part of the math necessary to find the new camera position. Once again, the math is a bit above my head, so
# I can't properly explain it. These blocks also set the move booleans to true so that the next lines will move the camera.
if moveY:
tempX = self.target.getX()+math.sin(angleradiansX1)*panRate1
tempX = self.clamp(tempX, self.panLimitsX.getX(), self.panLimitsX.getY())
self.target.setX(tempX)
tempY = self.target.getY()-math.cos(angleradiansX1)*panRate1
tempY = self.clamp(tempY, self.panLimitsY.getX(), self.panLimitsY.getY())
self.target.setY(tempY)
self.turnCameraAroundPoint(0,0)
if moveX:
tempX = self.target.getX()-math.sin(angleradiansX2)*panRate2
tempX = self.clamp(tempX, self.panLimitsX.getX(), self.panLimitsX.getY())
self.target.setX(tempX)
tempY = self.target.getY()+math.cos(angleradiansX2)*panRate2
tempY = self.clamp(tempY, self.panLimitsY.getX(), self.panLimitsY.getY())
self.target.setY(tempY)
self.turnCameraAroundPoint(0,0)
# These two blocks finalize the math necessary to find the new camera position and apply the transformation to the
# camera's TARGET. Then turnCameraAroundPoint is called with 0s for rotation, and it resets the camera position based
# on the position of the target. The x and y values are clamped to the pan limits before they are applied.
print(self.target)
self.mx=mpos.getX()
self.my=mpos.getY()
# The old mouse positions are updated to the current mouse position as the final step.
return task.cont 
