4.24: Drawing the Game State to the Screen

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$ $$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$$$\newcommand{\AA}{\unicode[.8,0]{x212B}}$$

        # Redraw the screen and wait a clock tick.
pygame.display.update()
FPSCLOCK.tick(FPS)


At this point, the game state has been updated depending on the player’s input, and the latest game state has been drawn to the DISPLAYSURF display Surface object. We’ve reached the end of the game loop, so we call pygame.display.update() to draw the DISPLAYSURF Surface object to the computer screen.

Line 9 set the FPS constant to the integer value 30, meaning we want the game to run (at most) at 30 frames per second. If we want the program to run faster, we can increase this number. If we want the program to run slower, we can decrease this number. It can even be set to a float value like 0.5, which will run the program at half a frame per second, that is, one frame per two seconds.

In order to run at 30 frames per second, each frame must be drawn in $$1 / 30^{th}$$ of a second. This means that pygame.display.update() and all the code in the game loop must execute in under 33.3 milliseconds. Any modern computer can do this easily with plenty of time left over. To prevent the program from running too fast, we call the tick() method of the pygame.Clock object in FPSCLOCK to have to it pause the program for the rest of the 33.3 milliseconds.

Since this is done at the very end of the game loop, it ensures that each iteration of the game loop takes (at least) 33.3 milliseconds. If for some reason the pygame.display.update() call and the code in the game loop takes longer than 33.3 milliseconds, then the tick() method will not wait at all and immediately return.

I’ve kept saying that the other functions would be explained later in the chapter. Now that we’ve gone over the main() function and you have an idea for how the general program works, let’s go into the details of all the other functions that are called from main().

4.24: Drawing the Game State to the Screen is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by LibreTexts.