Return to Question

These hills can form complicated structures for things like mountains:

I also want to be able to select tiles with mouse. I used this solution for a flat map:

1. This question. The proposed solution does not work because slopes may have different silhouettes so you can't simplify every tile into lines with same angles

2. This solution. As I understand, I'd have to create a second rectangular texture around each tile and use color data to represent central tile and its neighbours, but I don't think it would work well in my case because tile can be drawn far from its actual position due to height or it can be completely covered by a large hill in front of it.

Short version: I split my map into small chunks 100x100 pixels and use their red and green channels to store info about respective tiles

Full version: I have these fields in my TownLevel class with map:

I render an entire map to one texture and split it into chunks. I can't use full map by itself because SDL_RenderReadPixels() works too slowly with large textures. The full map is not necessary and can break my code on other systems due to SDL_Texture size limitations, I'll remove it later. Also, I use a Texture class for all textures. I create full map and chunks in the constructor:

These hills can form complicated structures for things like mountains: 

I also want to be able to select tiles with the mouse. I used this solution for a flat map:

1. This question. The proposed solution does not work because slopes may have different silhouettes so you can't simplify every tile into lines with the same angles.

2. This solution. As I understand, I'd have to create a second rectangular texture around each tile and use color data to represent the central tile and its neighbours. Still, I don't think it would work well in my case because the tile can be drawn far from its actual position due to height or a large hill can completely cover it in front of it.

Short version: I split my map into small chunks of 100x100 pixels and use their red and green channels to store info about respective tiles.

Full version: I have these fields in my TownLevel class with a map:

I render an entire map to one texture and split it into chunks. I can't use the full map by itself because SDL_RenderReadPixels() works too slowly with large textures. The full map is not necessary and can break my code on other systems due to SDL_Texture size limitations, I'll remove it later. Also, I use a Texture class for all textures. I created a full map and chunks in the constructor:

Is it possible to use 4 or 3 channels of a color? Current implementation limits map size to 256x256. My initial thought was to treat a single pixel as a 32-bit number, but SDL uses alpha channel for blending. Basically, I need to to overwrite destination with the color and alpha from the source if the alpha in the source pixel is not 0, is that possible to achieve with SDL_ComposeCustomBlendMode()? Or if it's impossible, how can I efficiently treat 3 channels as one 24-bit number or two 12-bit numbers without manual bit logic in the cycle?

Since I use only 2 channels of SDL_PIXELFORMAT_RGBA8888 pixel instead of 3 or 4, I limit size of the map to 2^16 instead of 2^24 or 2^32. How can I use pixel data more efficiently?

Questions:

1. Is it possible to use all 4 channels of a color? Current implementation limits map size to 256x256. My initial thought was to treat a single pixel as a 32-bit number, but SDL uses alpha channel for blending. Basically, I need to to overwrite destination with the color and alpha from the source if the alpha in the source pixel is not 0, is that possible to achieve with SDL_ComposeCustomBlendMode()?

2. If its impossible to use alpha channel, is it possible to efficiently use 8 bits from blue channel? If I could do it, I could make maps with the size up to 4096x4096, which is probably enough for me, but c++ doesn't have built-in 24- or 12-bit types and I'm not sure how to use 24 bits in this case.

3. Is this the optimal solution in general or am I overcomplicating things?

Question:

Is it possible to use 4 or 3 channels of a color? Current implementation limits map size to 256x256. My initial thought was to treat a single pixel as a 32-bit number, but SDL uses alpha channel for blending. Basically, I need to to overwrite destination with the color and alpha from the source if the alpha in the source pixel is not 0, is that possible to achieve with SDL_ComposeCustomBlendMode()? Or if it's impossible, how can I efficiently treat 3 channels as one 24-bit number or two 12-bit numbers without manual bit logic in the cycle?