Dark mode map in GMap.NET

Question

I'm developing an application using C# and WinForms, with GMap.NET library.

Would anyone know any way to set the dark mode for the map?

I'm currently using the OpenStreet map: map.MapProvider = OpenStreetMapProvider.Instance

I've looked in the documentation but I didn't find anything. When using Google map, it is possible to set color parameters in CSS, but I didn't find a way to define a CSS or theme directly in C#.

Answer 1

GMap.NET provides three predefined rendering modes:

• the default one, using the colors defined by the Provider
• An inverted mode, which sets the colors to negative => [GMapControl].NegativeMode
• A gray-scale mode, where all colors are converted to a scale of gray; white is white => [GMapControl].GrayScaleMode

These rendering modes use a ColorMatrix object to define the amount of color per channel.

It also provides means to specify a custom ColorMatrix, setting the [GMapControl].ColorMatrix property.

The inverted matrix is ~like this:

var matrixInverted = new ColorMatrix(new float[][] {
    new float[] { -1,  0,  0,  0,  0},
    new float[] {  0, -1,  0,  0,  0},
    new float[] {  0,  0, -1,  0,  0},
    new float[] {  0,  0,  0,  1,  0},
    new float[] {  1,  1,  1,  0,  1}
});

The gray-scale matrix is ~like this (my interpretation):

var matrixGray = new ColorMatrix(new float[][]
{
    new float[] { .2126f, .2126f, .2126f, 0, 0 },
    new float[] { .7152f, .7152f, .7152f, 0, 0 },
    new float[] { .0722f, .0722f, .0722f, 0, 0 },
    new float[] { 0, 0, 0, 1, 0 },
    new float[] { 1, 1, 1, 0, 1 }
});

If the negative mode is not exactly what you're looking for, you could invert the colors of the gray-scale ColorMatrix:

var matrixGrayInverted = new ColorMatrix(new float[][]
{
    new float[] { -.2126f, -.2126f, -.2126f, 0, 0 },
    new float[] { -.7152f, -.7152f, -.7152f, 0, 0 },
    new float[] { -.0722f, -.0722f, -.0722f, 0, 0 },
    new float[] { 0, 0, 0, 1, 0 },
    new float[] { 1, 1, 1, 0, 1 }
});

Then set the property:

[GMapControl].ColorMatrix = matrixGrayInverted;

About the usage of these matrices, see the notes in these questions:

How can I gray-out a disabled PictureBox used as Button?
How to use a slider control to adjust the brightness of a Bitmap?
How to apply a fade transition effect to Images using a Timer?
Replacing colour of an Image