Line/Shape colors and weights

[blasky]

Morning. Doing some drawing today on my NetVips images. Text and shapes.

Am I correct in my reading of the API that Image.Text() does not take an ink color? Do I need to write the text to my image and then somehow modify the color of what was just written?

And the shape methods, DrawLine(), DrawCircle(), etc., do take an ink color but they do not take a dpi value or line "thickness"? If I want a thicker line do I need to write multiple lines/shapes next to one another?

Thanks.

[kleisauke]

Hello @blasky,

Image.Text() makes a one-band mask image. It has no support for color. For colored text, you need to combine it with other operations. For example:

var text = Image.Text("<i>red</i> text color", dpi: 300);
text = text.Ifthenelse(new[] { 255, 0, 0 }, new[] { 0, 0, 0 }, blend: true);

var text2 = Image.Text("<i>red</i> background", dpi: 300);
text2 = text2.Ifthenelse(new[] { 0, 0, 0 }, new[] { 255, 0, 0 }, blend: true);

Image.Arrayjoin(new[] { text, text2 },
    across: 1, shim: 10, background: new double[] { 255, 255, 255 }).WriteToFile("text.png");

To make:

---

The image.Draw* operations are only really useful for very simple "paintbox"-style programs. I'd be cautious about using them anywhere else. The simplest solution for general drawing tasks is to load an SVG. For example:

var svg = @"
  <svg height='300' width='300'>
    <line x1='0' y1='0' x2='300' y2='300' stroke='black' stroke-width='3' />
    <circle cx='150' cy='150' r='140' stroke='black' stroke-width='3' fill='red' />
    <text x='50%' y='50%' dy='.5em' font-family='Arial' font-weight='bold' font-size='2em' text-anchor='middle' fill='white'>I love SVG!</text>
  </svg>";
var image = Image.SvgloadBuffer(Encoding.UTF8.GetBytes(svg), access: Enums.Access.Sequential);
image.WriteToFile("shapes-and-text.png");

To make:

The libvips SVG loader is very fast and can make images of any size. It renders progressively, so it doesn't need much memory either.

Use the boolean operators to mask other images with the result, or use image.Composite to layer images together with the PDF blend modes.

[blasky]

Makes perfect sense. Will do. Thank you.

[kleisauke]

Hope this helped, please feel free to re-open if questions remain.