Graphics and Animation - Invent Your Own Computer Games with Python - page 321

17 - Graphics and Animation
40))
The pygame.draw.rect() function will draw a rectangle. The third parameter is a
tuple of four ints for the left, top, width, and height of the rectangle. Instead of a tuple of four
ints for the third parameter, you can also pass a Rect object. In line 45, we want the
rectangle we draw to be 20 pixels around all the sides of the text. This is why we want the
drawn rectangle's left and top to be the left and top of textRect minus 20 . (Remember,
we subtract because coordinates decrease as you go left and up.) And the width and height
will be equal to the width and height of the textRect plus 40 (because the left and top
were moved back 20 pixels, so we need to make up for that space).
The pygame.PixelArray Data Type
47. # get a pixel array of the surface
48. pixArray = pygame.PixelArray(windowSurface)
49. pixArray[480][380] = BLACK
On line 48 we create a pygame.PixelArray object (which we will just call a
PixelArray object for short). The PixelArray object is a list of lists of color tuples
that represents the Surface object you passed it. We passed windowSurface object
when we called the PixelArray() constructor function on line 48, so assigning BLACK
to pixArray[480][380] will change the pixel at the coordinates (480, 380) to be a
black pixel. Pygame will automatically modify the windowSurface object with this
change.
The first index in the PixelArray object is for the X-coordinate. The second index is
for the Y-coordinate. PixelArray objects make it easy to set individual pixels on a
PixelArray object to a specific color.
50. del pixArray
Creating a PixelArray object from a Surface object will lock that Surface object.
Locked means that no blit() function calls (described next) can be made on that
Surface object. To unlock the Surface object, you must delete the PixelArray
object with the del operator. If you forget to delete the Surface object, you will get an
error message that says pygame.error: Surfaces must not be locked
during blit .