Tkinter - Random Backgrounds with Python, version 2!

Our original random background generator was rife with errors so we've restructured it to make it a little better. See if you can follow the math and where I went wrong in the last one!

Pyglet - Keymapping and Sound effects

For any real game however you probably want some conditional events - like controlling an object or causing something to happen when a button is pressed. In the below example we map three keys; a, left arrow and the left mouse button to 3 separate actions.


A couple of things to note:

• to ensure the sound effect plays at the same time as the key is clicked we load the resource into memory instead of streaming the audio file as we did in the earlier example.
• for keymapping the 'modifiers' field indicates where Caps, Shift or Ctrl is held.
• Finally for mouse events and x and y is returned giving the location of the mouse cursor in the window when pressed.

Challenge!

Using this sounds effect, create a game that creates yellow ovals at the mirrored mouse location when the left button is pressed. I.e. if a mouse click was at (200, 100) in a 600x800 window then the 'mirrored' location should be at (600-200, 800-100).

Pyglet - placing images, text and playing background music

Continuing on our Pyglet introduction you can use the basic environment we set up earlier to place external images (in a few different formats), display text and to add some atmospheric background music. This code is pretty self explanatory so I'll just post the lot and let you dig through it yourself - but one thing to notice is that by itself pyglet/Python can't decode and play .mp3 audio files. It requires an external library called AVBin. So if you get an error when trying to play .mp3 files try installing the AVBin library (see the link below for details).


There are a few other commands in here that are worth pointing out:

• image.blit(0,0) - the (0,0) is the location of the centre of the image  in x and y co-codinates. 'Blitting' is the process of drawing an image into our window. Otherwise we only load it into memory and never display it.
• we also use the window.height and the window.width commands to return the current height/width of the window which is a far nicer way of defining the location of things. (N.B. the height and width methods also work on image objects!)

Challenge!

Find some nice atmospheric music for your game (and yes check it's Creative Commons licenced for you to use first!) and setup a background image you want to use and display it in the centre of your image in such a way that if you resize your window it appears in the the same place. I highly recommend checking out the wonderful local composer Rhian Sheehan's Soundcloud for inspiration (and yes you can download some of his .mp3s but make sure to attribute them if you use them!). 

References

http://www.pyglet.org/doc/programming_guide/playing_sounds_and_music.html

Pyglet - moving, rotating and translating images in 2D

Continuing on from the previous tutorial, now we can dig into moving things around in 2D. Why bother learning this when I've covered the same thing in Tkinter tut and when I'm going to cover it again in a pygame tut? Because in pyglet, the same commands for movement and rotation in 2D ALSO APPLY TO 3D, so once we make the jump to 3D we will automatically have access to all the colours, motion and movement actions we're already learned rather than having to grapple with all of them together at once. *

Translation

The translation command takes an object you've created and then moves it by a certain amount. In the previous tut, we controlled the shape and size of our triangle by where we placed it, but imagine if we wanted to move it after we had created it. Then we would have to calculate the location of all the vertices of the object every time it moved. So instead, we create an image close to our origin and use that to control its size and shape and then we move it to where we want in a separate command. This comes in really handy in 3D when figuring out where things are in 3D space and describing that in detail does my head in - so i cheat and use this command instead:

glTranslatef()

The three numbers we pass the method tell OpenGL how far and in what direction we want to move our shape in the order x,y,z. Some helpful tips to remember:

• x = left or right motion. Negative numbers move left, positive moves right.
• y = up or down motion. Negative numbers move down, positive moves up.
• z = motion into or out of the screen (3D only), Negative numbers move into the screen, positive moves out of it.

And yes, because we're in 2D all our transformations currently will leave z =0.0. Try changing it if you like and see what happens, but it's likely your image will disappear because we haven't quite set our system up to display 3D well yet.

Rotation

Rotation is similar to translation except it requires some serious math. So once again, rather than bothering with the details we use an OpenGL command to do all the heavy thinking for us. This time though we have 4 input options:

glRotatef(10.0,0.0,0.0,1.0)

They're:

1. the number of degrees to move
2. 1.0 if rotating around the x axis, 0.0 if not
3. 1.0 if rotating around the y axis, 0.0 if not
4. 1.0 if rotating around the z axis, 0.0 if not

So a full program making use of both translation and rotation would looks something like:

Note: We've also included 2 other commands 

    glMatrixMode(GL_MODELVIEW)

    glLoadIdentity()

These aren't explicitly necessary - take them out and everything will still work fine. However, once we move into more complicated motion these will become really important, because we're going to have to change between viewpoints and these are the command that 'bring us home' (i.e. back to where we started). For those that are interested, OpenGL works by using a matrix to transform/move/rotate our objects depending of our starting position. If we move to a new location then the same matrix will have a different effect - so we 'come home' by loading the identity matrix in case we've accidentally changed location without realising it. Yes this is why linear algebra is important for computer graphics. No it's not the only reason - but it's one of the prettiest. :) 

Challenge!

Does the order of the translation and the rotation commands matter? Is that weird? Can you figure out why or why not? What happens to your image if you rotate it around the x or y axis? Why?

Movement

Time for another method that I mentioned earlier - update().

def update(dt):

    global rz

    rz += dt * 10

    rz %= 360

ry=0

pyglet.clock.schedule(update)

The update() command every time pyglet's internal clock 'ticks', so if we change the position just a little with every 'tick' as long as it happens fast enough this will look like movement. Here's we're probably better to explain by example:

The details are - we create a global variable called rz (the rotation around the z direction)

Challenge!
What happens if you set rz to be constant??? Why? What would you need to add to get translation working?

*I'm certain this can also be achieved in pygame with or without external libraries (see examples here) and if I ever learn how with that I'll post a tutorial on it.

Tkinter - Random Backgrounds with Python

Ever tried to design your own game? It can be a tricky process though so I’ll walk you through it using an example. You can either copy the example and modify it to make it more like what you want or try something different. I would recommend following along with these examples first though to see what you can expect.

We’re going to start by creating a 2D game, with a randomly generated background that you have to move your character through to get to the exit. Once that’s done we will add some monsters to chase your character and then the sky’s the limit! Diagrammatically it might look like this:

I’m going to start by creating a randomly generated forest with some rocks and trees (similar to what you might find in old school pokemon games).  First off go find some objects you want to randomly scatter around your map. Remember they should be .gif images!

If you’re looking for some code to use an example try this (yes I used stones and trees because I’m a farm boy)

So you now have a randomly generated background each time you run the programme. The problem is that, well, it kinda sucks. It would be better if we could stop trees and rocks from appearing in the same place wouldn’t it? And if they didn’t disappear off the edge of the map?

Whoa! That got really horrible really quickly didn’t it. If you poke through the code above you might be able to understand what I was doing. I made a list of all the locations I had placed each tree and just checked that the distance between those locations and any new location was greater than the width of the new image I was adding. Unfortunately it’s easy for this sort of structure to get stuck in an infinite loop (as the computer is just randomly guessing each time where to place things). 

 

CHALLENGE #5!

Can you imagine a better way to decide where to place our new trees? Is there a maximum number of trees/rocks we can fit into our window? How might we figure it out? (Hint: this becomes a lot easier if we re-visit this after we’ve learned object orientation)

CHALLENGE #6!

 If we were creating a real level we wouldn’t want things placed randomly. Objects have rules. Imagine trying to create a river through our field. The rule is that from a starting location the river can only be extended into a location that’s next to a bit that’s already river. Can you think about how we might some code to figure this out?

Tkinter - Python games with Tkinter

Note: I would only use Tkinter to create games if you have an issue installing external python libraries to your system or if you're using Python 3 rather than Python 2. Otherwise the specific game libraries pygame or pyglt are both superior and easier to learn. There are introductory tutorials to both of these in the sidebar.

Why Tkinter and what is it?

Tkinter is a python library that comes standard with both Python 2 and Python 3 for generating Graphical user interfaces (GUIs). It's ubiquity is its strength more than anything else and I frequently resort to Tkinter when I can't get other libraries installed (a common problem for many Digital Technology classes here in NZ).

Making windows and objects

Open IDLE (if you don’t have it download and install it from here - you want the Python 3.4.0), select a ‘New File’ from the file menu. This is where we will write the majority of our code. the other window is called a ‘shell’ and allows you to interact with your program - but it will make things more complicated than they need to be so we’ll leave it alone for now.

If this is your first time programming - here are 4 things to know:

    1) spelling and capitalization are crucially important. If your code doesn’t work check your spelling

    2) in python, indentation is important. Code from this tut should be copied directly with indents preserved. If your code doesn’t work, check your indents are right.

    3) Patience. You will make mistakes. Lots of them. They will irritate you. You will stop making them, but only through practice. If you’re getting irritated stop and try something else for a while!

    4) Google it. Seriously. Any problem you have - google it and pick the result (look for a website called stack overflow) and chances are you will find a solution.

Get started - make a window

Copy and paste the following code into the window:


Then select ‘Run’ from the file menu above or push F5 on your keyboard (or fn and F5 on OSX). If you get an import error (i.e. your console says something like 'cannot find Tkinter module') try changing the import statement from import Tkinter (for Python 2.7) to import tkinter (Python3)

You made a window!

Filling the window 

Try replacing your code with this instead, and hit Run. Time for a bit of explanation!

You’re doing several things:
    creating a window:
                         Window = Tk()

    filling the window with something you can draw on:
                         canvas = Canvas(height=500, width=500, bg='red')
                         canvas.pack()

    creating a rectangle in that canvas:
                        canvas.create_rectangle(200,200,300,300, fill='blue', activefill='green') #x1,y1,x2,y2
                       (N.B. you can make lots of other shapes using: create_oval, create_arc, create_line etc)

    then running our program:

                         Window.mainloop()

If you care about any of this (or want to know more!) - just ask Elf google it.

Good news: you don’t need to understand it to use it!

CHALLENGE #1!

Make a 400x 400 pixel window with a green background that has a smiley face on it.

Adding images

Find an image from somewhere that is in .gif format (or find an online converter). Put it in the same directory as where your python file is saved and give it the name ‘image.gif’

Now try this code:




What do you need to change to move your image around your canvas?

Duplicates

OK now we’re going to do some more advanced programming. Why? Because we want lots of images in lots of places rather than just one. We’re going to use a loop to do that (specifically a for loop). Here’s your code:

Random

Now to explain that ‘import’ statement up the top. When programming it’s common to use bits of code other people have made. These are called libraries and we’re already using one called Tkinter. Now we need to use another one called random which will allow us to generate random numbers (yes exactly like playing calculator cricket). Try this:





and now your images are randomly located all over the map :) Note that we’ve also slightly changed our for loop.

CHALLENGE #2!

Make 20 ovals of random sizes and locations all over your canvas

Movement!

So random placement is ok - but movement would be better. To start we’re going back to moving one image at a time in the interest of simplicity. We’re going to do this by DEFINING two VARIABLEs for the position of our image. Then we’re going to re-draw our image each time it moves and updates our canvas.

Advanced movement

So moving things is ok - but when really want them to move forever, not just for a set period of time. For this we will need a new structure called a while loop.

Boundaries

Now we can add another kind of programming tool called an if statement (or a conditional statement). These allow us to specify different actions depending on what’s going on! Try this:





Whoa?! That’s a bunch of new code. All it’s doing is saying that whenever your object gets to the edges of our window we change it’s speed. See if you can follow through the logic (but again don’t worry if you can’t). To give you a clue - the x and y are position VARIABLES (they remember where on the screen our object is) and the dx and dy are how fast to move in either the left or right direction or the up and down direction respectively.

Keyboard control!

To really make this a game though we want you to be able to control aspect of your character with either the mouse or keyboard. We’re going to do this by making the up arrow on the keyboard make the object move faster and the down key do the opposite.

Try it out. What do you notice? Can you find the bug?

Once again - if this doesn't work and your error message say something about '<key>' in the .bind() command above change <key> to <Key> and it should work.

We’ve used a heap more code this time and something called a ‘method’. It’s quite a bit more complicated and so once again - if you don’t understand don’t worry! However, the bad news is that we’ve reached the limit of what we can do programming as we have been. To go further we’re going to have to think about our programs in a way called ‘Object Oriented Programming’. Think about it like this: in our example above we keep variables for the speed and position of our character. If we had multiple characters we would have to make all these again for all of them and the number would quickly become unmanageable (so would the code for that matter!) - so we need a new way of thinking about things. We will do this by creating objects and getting each object to remember its own speed and position.

From here you have a few choices - continue with the more complicated programming (which will be useful for any language or game you use in the future), move onto something else like unity or blender, or spend some time designing your game and use what you’ve learned above to make a randomly generated background.