Need to change image each frame

[parallax7d]

I need to generate an image, and render it each frame. This is for a particle simulation with lots of moving pixels.

I put love.graphics.newImage under love.update and while it did reload the image each frame, it was at an unusable framerate.

Would it be possible to load a new image once - then manipulate it in ram directly? That way I can redraw the image each loop without having to call newImage every frame? Or is there a simpler method I'm missing?

[slime]

You can do something like this:

Code: Select all

function love.load()
    imagedata = love.image.newImageData("myimage.png")
    image = love.graphics.newImage(imagedata)
end

function love.update(dt)
    imagedata:mapPixel(mymapfunction)

    -- Updates the image's contents in VRAM with the ImageData's latest changes.
    image:refresh()
end

function love.draw()
    love.graphics.draw(image)
end

But CPU-side pixel modifications will always be slow. I recommend drawing to a Canvas instead, if possible. It will be orders of magnitude faster.

[parallax7d]

Unfortunately for my needs that method would be too slow like you said. The image:refresh() method looks promising though! It seems to be working at least 100x faster than a full graphics.newImage call. thanks!

[parallax7d]

Is there any way for love to display an image from a memory region of my choosing? I'm assuming it's caching a copy on it's own? I would rather it just reference mine directly if possible.

[slime]

Images live in video memory and are owned by OpenGL / the video driver. The driver will often arrange the contents of the image in VRAM such that its data is tiled rather than linear, for more efficient drawing.
Using a CPU-side linear memory directly as an OpenGL texture generally isn't possible.

As an aside, you can use this drop-in script to make ImageData methods more efficient without changing your own code: https://github.com/slime73/love-snippet ... ta-ffi.lua

[parallax7d]

Just to clarify, so when we use love.graphics.newImage, is it not caching anything into system ram, it's uploading directly to the vram?

[slime]

Right - the love.graphics Image creates and owns a reference to a texture in VRAM. It also keeps a reference to the ImageData which was used to create the Image (ImageData objects reside purely in RAM.)

When you call Image:refresh, it re-uploads the ImageData's contents in RAM to the texture in VRAM.

Keep in mind OpenGL (and other graphics APIs) abstract away the notion of VRAM, since many GPUs don't even have dedicated VRAM. love.graphics.newImage just tells OpenGL to create a texture using the contents of the ImageData, and it doesn't really know where the OpenGL texture will be stored (but the graphics driver will put it in VRAM if possible.)