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SDL selection based on color


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#1 OliverNordbjerg   Members   -  Reputation: 100

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Posted 22 April 2012 - 07:28 AM

Hello GameDever!

I am trying to create a game, in which you play a country with a number of provinces, but for this game to work, I need to have a way to select these provinces. I thought of making every province easy to identify by using unique colors (from a devers point of view), but of course, I do only want to use these colors internally, and they shouldn't be rendered.

I thought of checking the pixel you are currently clicking on, and looking for the province with the color of the pixel in a table, containing pointers to all of the provinces. This seems fairly straight forward, but how do I get the unique color of the province, when I am rendering it with a different color?

This problem will be easier to understand for people who have played some of Paradox Interactives games before, because they also use a similar layout (I think).

Also, I will be using SDL for this.

Oliver

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#2 GameGeezer   Members   -  Reputation: 778

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Posted 22 April 2012 - 08:37 PM

Have a generic country object that either has a name or id you can use to idenify each country with. when a player clicks on the object check to see if that point is contained within the shape, if it is then select that country. Your method sounds a bit messy to say the least, I would really rethink how you're approaching the problem.

#3 SimonForsman   Crossbones+   -  Reputation: 6288

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Posted 22 April 2012 - 09:52 PM

Hello GameDever!

I am trying to create a game, in which you play a country with a number of provinces, but for this game to work, I need to have a way to select these provinces. I thought of making every province easy to identify by using unique colors (from a devers point of view), but of course, I do only want to use these colors internally, and they shouldn't be rendered.

I thought of checking the pixel you are currently clicking on, and looking for the province with the color of the pixel in a table, containing pointers to all of the provinces. This seems fairly straight forward, but how do I get the unique color of the province, when I am rendering it with a different color?

This problem will be easier to understand for people who have played some of Paradox Interactives games before, because they also use a similar layout (I think).

Also, I will be using SDL for this.

Oliver


Create a second (software) surface (hardware surfaces are slow to read from) with the colorkeyed version of the map and read the colors from that surface (don't render it).

You can probably use a lower resolution for this map aswell to save memory (just remember to properly scale down the mouse position aswell before reading the keyed map though)

Edit:
Here is a link with info on how to access surface pixels with SDL: http://www.libsdl.or...gi/Pixel_Access
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#4 OliverNordbjerg   Members   -  Reputation: 100

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Posted 23 April 2012 - 03:37 AM

Have a generic country object that either has a name or id you can use to idenify each country with. when a player clicks on the object check to see if that point is contained within the shape, if it is then select that country. Your method sounds a bit messy to say the least, I would really rethink how you're approaching the problem.


I thought of your approach, but I am worried that it will eat my CPU, and I am going to need that for other stuff.


Create a second (software) surface (hardware surfaces are slow to read from) with the colorkeyed version of the map and read the colors from that surface (don't render it).

You can probably use a lower resolution for this map aswell to save memory (just remember to properly scale down the mouse position aswell before reading the keyed map though)

Edit:
Here is a link with info on how to access surface pixels with SDL: http://www.libsdl.or...gi/Pixel_Access


Thank you, I will use this approach.




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