Game Development Reference
In-Depth Information
Although this could be done with
if
statements, as the complexity of the system
increases these statements would become increasingly complex. A better solution
is to use a
clamp
function, which takes a value and restricts it to be between a
minimum and maximum value. In this case, we want the camera's x-position to
be equal to the player's x-position, with a minimum valid value of half the screen
width and a maximum valid value of the center of the final background.
Once we have the position of the camera, we can then determine which back-
groundsarevisiblebasedonthecamera.Finally,allthesprites,includingtheback-
grounds, can be drawn with an offset based on this camera position.
// camera.x is player.x as long as its clamped
within the valid range
camera.x
= clamp(
player.x
,
screenWidth
/ 2,
hCount
*
screenWidth
-
screenWidth
/ 2)
Iterator
i
=
bgSpriteList
.begin()
while
i
!=
bgSpriteList
.end()
Sprite
s
=
i
.value()
// find the first bg image to draw
if
(
camera.x
-
s.x
) <
screenWidth
// Image 1: s.x = 0, camera.x = 480,
screenWidth/2 = 480
// 0 - 480 + 480 = 0
draw
s
at (
s.x
-
camera.x
+
screenWidth
/2, 0)
//
draw the bg image after this, since it
might also be visible
i
++
s =
i
.value()
draw
s
at (
s.x
-
camera.x
+
screenWidth
/2, 0)
break
end
i
++
loop
This provided code implements scrolling where the camera and player can move
forward and backward through the level, as in games such as
Super Mario World
.
