Rusttype rasterize font and display text

help
1

I am confused about the rusttype crate. I can understand how the simple example works to create ascii art from text by mapping characters as pixel points, but I just want to display text in a window. What would you do instead of this:

let mut pixel_data = vec![b'@'; width * pixel_height];
2

Which gui library are you using?

3

minifb

Right now the only way I'm getting text to display is by putting the text into a string formatted as SVG, use resvg to convert that to a png and then displaying the png in the minifb window. I recognize how very wrong that is but I've not been able to figure out how the various glyph libraries generate pixel buffers that minifb can read.

4

Iirc there's an "image" example that writes to a Vec pixel grid. Maybe that's closer to what you want?

5

I guess I'm not clear on how to get the information supplied by the png::Decoder in that example without first saving the svg as a png file. I think the png crate documentation assumes a level of baseline knowledge that I don't possess.

6

I assume you would use Window::update_with_buffer if you're using minifb? In that case you can create a vector of u32 for the image data, and then call draw on your glyph, and inside the closure, write into the vector.

It would probably look like this, but I have not tested it:

/// from update_with_buffer example
fn from_u8_rgb(r: u8, g: u8, b: u8) -> u32 {
    let (r, g, b) = (r as u32, g as u32, b as u32);
    (r << 16) | (g << 8) | b
}

let mut vec = vec![0; width * height];
glyph.draw(|x, y, v| {
    let idx = (x + width * y) as usize;
    let brightness = (v * 255.0) as u8;
    // same r, g and b gives grayscale
    vec[idx] = from_u8_rgb(brightness, brightness, brightness);
});

// Update window
window.update_with_buffer(&vec, width, height)?;
1 Like
7

Thanks. I think you've got me on the right track, but I'm having a hard time getting the proper values for width and height, I think. for a single glyph I'm using width and height of 13 and 12 and get an error of "Required size for 13 (13 stride) x 12 buffer is 624 bytes but the size of the input buffer has the size 156 bytes".

8

Sounds that you tried to allocate a byte for each pixel, but 4-byte pixel values was expected. So for a byte buffer (a Vec<u8>) you need lenght width*height*4. OR you might be able to use a Vec<u32> or even some kind of Vec<Pixel> instead.

9

That did the trick (mostly). Still working on some quirks like the text not being crisp and being repeated four times, but it displays.

10

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