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How to GM using GIMP

PostPosted: 07 Mar 2019, 20:07
by joe92
How to GM Using GIMP

We have two new aspiring GM's and I'm sure more will be looking to take the leap into GM'ing in the future so I have taken the time to write this guide on how to GM using GIMP. GIMP is a free-to-use open source image manipulation program similar to Photoshop and Fireworks. While GM'ing might seem like a daunting task and this guide might look long and scary, the manipulation of images is actually pretty easy once you know how to do it. For example, during the last game of ModEx, a map with 14 players and 91 supply centres - thus 91 sets of orders - it would take me an average of 40 minutes to adjudicate the orders and about 5 minutes to adjust the map.

For this guide I will be using the Heptarchy map as an example. It is a map many people are familiar with. Just extract the methods explained within to use on whatever map you want.

This is an interactive guide. Please make sure you have downloaded GIMP, then follow this link to download the .xcf file for Heptarchy. You will understand things much quicker if you work on the map at the same time as reading the guide.

Please note: While this guide does explain some rudimentary adjustments to maps, this is not a guide on how to create maps. It is solely about using GIMP to GM.

1. Understanding Layers
2. Moving Units
3. Recolouring Territories
4. Handling Retreats
5. Building and Destroying Units
6. Saving to PNG
Bonus: Tips and Tricks

1. Understanding Layers

The first step to GM'ing in an image manipulation program is understanding layers. A lot of what you do is through controlling layers correctly. For the Heptarchy map the Layers Panel looks like so:


The order of the layers, and groups, is crucially important. Any layer or group that is above another layer or group will have their pixels superseded over the layers below. Think of it like this, when creating the image it will print out the bottom layer, then it will print the layer above that over it and so on until it has printed the top layer. In my mind when it comes to layers the more the better, however you could theoretically GM just fine having just 3 layers: 1. Units, 2. Territory Names and Supply Centres, 3. Map.

However, we'll stick with my Heptarchy example for now. The layers are as so:

Units - This is a layer group. Within this layer group there are 8 more layer groups. The first 7 groups are the layer groups which contain the units for each power and the 8th layer group manages retreats.
Territory Names - Land - This is a layer group. It contains all the text layers for the land-based territory names.
Territory Names - Sea - This is a layer group. It unsurprisingly contains all the text layers for the sea-based territory names. It wasn't actually necessary to do it like this. It just makes it easier to compartmentalise so I can find a particular territory name quicker.
Supply Centres - This is a layer group. It contains all the icons for the supply centres on the map.
Heptarchy ... - This is a text layer. It is the white watermark in the top right of the image which contains the variant name, the number of supply centres and number needed to win, the map creator and who did the latest render, me.
Heptarchy-blank-canvas.png - This is an image layer. This is the base image of the map. It is 95% of what you see in the end. It is all the colours on the map and all the lines partitioning the different territories.

Because of the layering hierarchy, any unit which is in the same place as a territory name will obscure that name, territory names will obscure supply centres, and they all obscure tiny sections of the map. If you were to put the map layer to the top, all you would see is the map.

To create a new layer you simply click on the bottom left icon of a page with a plus in the corner. Name the layer, make sure the layer fill type is set to transparency (this ensures any pixels not used are see through to the layer beneath) and click OK. Note: you cannot name any 2 layers the same. Hence you will see below that all the layers for units are numbered.

To create a new layer group, simply click on the bottom second-to-left icon of a folder. This will insert a new layer group. To rename it to something helpful click on the new group, press F2, type in the new name and hit enter.

That's it for layers. It's pretty easy. Just remember the hierarchy.

2. Moving Units

Ok, it's the first spring of the game. Among all the orders you received there is an order to move Northumberland's army in Durham to Wolds. First things first. You have to locate the layer which contains the Durham army. To do this, expand the Units group then expand the Northumberland group. It will look something like this:


Naming the layers according to the territory the unit is in makes no sense as units move around and you would waste a lot of time renaming layers. Instead there are 2 methods to quickly identify which layer the unit belongs to.

Method 1 - Click on the Visibility icon (the eye) to turn the layer off. Click it again to turn it back on. Toggle the layer on and off while looking at the map to determine which unit it represents. Repeat this going down the list of units until you have found the necessary layer. This method is pretty quick while there aren't many units on the map.
Method 2 - Select the Move Tool from the toolbox (shown below). Move your mouse to the unit you intend to move, then click and hold the unit without moving the mouse while looking at the Layer Panel. The layer which you are selecting will have been highlighted. Let go of the unit, then select that layer. This method is preferable once you have lots of units on the board.

With the necessary layer active, ensure you have the Move Tool selected. It is the blue cross with four arrows, it looks like so:

Shortcut: Press 'M'

Now move the unit. Like finding the correct layer, there are 2 methods to moving the unit.

Method 1 - Click and drag the layer. Using you mouse, hover over the unit, click and hold, and drag your mouse to the desired new location. This method is preferable if the unit has a long way to move.
Method 2 - Use the keyboard. Click once on the image without moving the mouse to focus back on the image. It doesn't matter if you click on the map layer, when you unclick the unit layer will automatically be reselected. Use the keyboard directional arrows to move left, right, up or down. This will move the unit along ever so slightly with each press. This method is needed to get that greater accuracy for placing the unit to ensure it isn't obscuring the territory name while still clearly contained within the territory. If you hold shift while using this method it will move the unit further with each press.

You will mostly need a combination of the methods above to place the unit in the perfect position.

3. Recolouring Territories

One of the best things about playing diplomacy online is the recolouring of territories that happens while your units move around. It greatly helps to visualise what's happening. As a GM, as long as the boundaries on the map are solid it only takes a few seconds to do it. So do it.

Durham has just landed in Wolds. This is a neutral territory so you can recolour it whether it's spring or autumn. First things first. Make sure you are on the right layer. The map is at the very bottom so no tricks needed, just select the map layer. It's worth noting that apart from the Move Tool every other tool will only affect the layer you are on. With that done now select the Colour Picker Tool from the toolbox.

Shortcut: Press 'O'

Hover over a Northumberland territory, i.e. Durham. Click. You will see the colour palette in the toolbox change to the desired colour. With the colour in the palette, select the Bucket Fill Tool from the toolbox.

Shortcut: Press 'Shift + B'

Hover the cursor over Wolds and click to fill with the Northumberland colour. This will recolour all similarly coloured pixels in that area to be the same as the palette. Which means until it hits the black lines demarkating the territory it will change all those white pixels to yellow. If you have a break in the boundary lines you will bleed over and recolour other territories, so just make sure they are solid. Because the tool only affects the layer you are on, it doesn't even matter whether you accidentally click on the unit. It will click through that to the map layer selected.

4. Handling Retreats

As a player I want to be able to see the retreats easily. As a GM I want the retreats to be easily identifiable to avoid any dispute among players claiming they didn't know they had a retreat.

One method used is to place the retreating unit beneath the attacking unit. It has many times caused issues in games with players not knowing they had to retreat because they didn't read the list of orders. Let's not discuss how foolish it is to not read the list of orders, just know that it happens, a lot.

If you've played in one of my games you know that I add flames or crosses to the map to indicate which units must retreat. It's actually very simple and takes just a tiny amount longer than sorting the hierarchy to place a unit beneath another. In the Heptarchy game the flames don't look good sitting on top of a human head, so I created crosses for that game.

Keeping our scenario going, let's say that in the spring Mercia moved King's Lynn to The Wash and Nottingham to Lincolnshire. Ignoring the strategy of such moves, move those pieces on the board and recolour Lincolnshire as necessary. Now the autumn has come around lets say Mercia gave the order for The Wash to support Lincolnshire to Wolds while Northumberland tried to move Wolds to Lincolnshire unsupported. Mercia is obviously successful in this attack and Northumberland will be requested to retreat.

Step 1 is to move the units. Move the Mercian army in Lincolnshire to take the space of the army in Wolds. Move the Northumberland army in Wolds to further up in the Wolds. Use the keyboard method described above. Click on the image and use the arrows.

Step 2 is to move the layer for the Northumberland army in Wolds into the Retreats group. First expand the Units layer group, then expand the Retreats layer group. You will see a bunch of hidden X icons and at the bottom there is yet another group called Retreating Units.


What you need to do is click and drag the layer for the retreating Northumberland army into that Retreating Units group within the Retreats group. It's very simply just a click and drag on the name of the layer. If you get towards the bottom of the Layer Panel it will start automatically scrolling for you. Once your mouse is over the Retreating Units layer with no black line shown above or below it (that black line indicates it will go above or below the group, not in it), let go. The unit will be in the folder but will have disappeared from view as the Retreats folder has visibility turned off.

Step 3 is to place the cross icon over the unit. Toggle the visibility of the entire Retreats group. There are 4 icons for the crosses, they will appear in the top left of the map. Turn the visibility off for all but one of those crosses. Now select the correct layer and use the Move Tool to move that cross to be positioned over the retreating Northumberland army.

Step 4 is to not forget about recolouring the territory if it is a neutral one or the end of a year. The crosses or flames or whatever icon you use do help immensely with seeing where the retreat is. If the unit contrasts against the background colour it helps even more. The end result will look like this:


After the retreat has been issued remember to move the retreating unit's layer back into the correct group, and to disable visibility for the Retreats group to hide the crosses.

5. Building and Destroying Units

Because we are using layers, this is by far the quickest and easiest part.

Building Units
If the user has requested a new army, find an army layer for that power, right click on the layer name and select Duplicate Layer (or click the Duplicate Layer icon at the bottom of the Layers Panel, third from the right). A new layer will appear above the one you just duplicated with the word 'copy' at the end. E.g.


You can just call it copy if you want, but I have found it very helpful to rename them with the latest increment of the number of armies. To do that click on the layer, press F2, enter the new name and press enter. If you know no units have been disbanded during the year it helps you count the number of units on the board.

Now just move the newly created unit to the build location.

Destroying Units
If a user has requested to destroy a particular unit, locate the layer using the method described above. Once found, simply right click and select Delete Layer (or click the Delete Layer icon at the bottom right of the Layers Panel). The layer containing the unit has been deleted. That unit has been destroyed.

Tip: If the players is deleting their last army or their last fleet, I will simply toggle the visibility of that unit just in case they build a new one in the future. In fact, if you look in the Anglia Unit group you will see there is a fleet on standby with the visibility turned off.

6. Saving to PNG

Firstly, an explanation. The site recommends to save to GIF. I recommend to save to PNG. The reason for that is simply that PNG-8 has a better compression rate once you are compressing down to something over the size of 30kb. Since it is extremely unlikely you will be able to compress below 30kb PNG-8 will be better. If you want to read more on different image formats for the web this question on Stackoverflow answers it very well.

The method to save to an image is as so.

1. First make sure you have saved your .xcf file. Press Ctrl + S. The * before the file name in the top of the window will disappear.
2. In the top menu options click Image -> Flatten Image. This will merge all the different layers into 1 single layer.
3. In the top menu options click Image -> Mode -> Indexed. A pop up will appear with some options. You don't need to mess with them. Leave as default and press "Convert".
4. In the top menu options click File -> Export As. Shortcut: 'Crtl + Shift + E'
5. The Export Image window will have popped up. Make sure that the file extension for the image is .png and press Export. Another popup will have appeared. Set the "Compression level" to maximum and click Export (it will remember your choice of Compression level hereon out).
6. Important: Press "Ctrl + Z" two times until the file name no longer has the * in it. Alternatively, close GIMP and select "Discard Changes". You do not want to save your GIMP file with all the layers flattened!


In the future I imagine that GIMP will introduce a method to export an image with the layers flattened without having to manually flatten the layers, index the colours then unflatten them, like Adobe Fireworks already does. That would make this step considerably easier. Until then you have to go through this method. If you followed this method correctly, flattening the image, indexing the colours and exporting as a PNG file you should see that the PNG image it created is less than 50kb in size. Well within the site restrictions. Upload that to the forum with the corresponding orders and you're good to go!

Bonus: Tips and Tricks

I've run out of time and will get some additional tips and tricks in at some point in the future. The above guide is all you need to get on GM'ing. I hope this has helped someone out there!

Re: How to GM using GIMP

PostPosted: 07 Mar 2019, 20:31
by Elric Hazard
It has already helped me finally understand layers and their usefulness in general, so thanks Joe92.

Re: How to GM using GIMP

PostPosted: 08 Mar 2019, 02:37
by VGhost
Oh good, somebody finally put together something better than my slap-dash version. Props to joe.

Re: How to GM using GIMP

PostPosted: 11 Mar 2019, 11:28
by joe92
Elric Hazard wrote:It has already helped me finally understand layers and their usefulness in general, so thanks Joe92.

Glad to hear it's helped someone already 8-)

GhostEcho wrote:Oh good, somebody finally put together something better than my slap-dash version. Props to joe.

Thanks. Though I would say our guides compliment each other rather than compete. Yours covers more of the map making methodology whereas this is exclusively for the purpose of GM'ing assuming the map is already made :)

Re: How to GM using GIMP

PostPosted: 12 Mar 2019, 01:48
by NoPunIn10Did
This is excellent, Joe.

And for those that want to use any of the existing SVG resources for maps in Inkscape, it's not actually vastly different. You turn on and off layers, you move units around, and you select new colors for regions. Then you export.

Now building a new map with either Inkscape or GIMP is a whole 'nother topic...