.net – Insert Space Between Pixels

.netgdi+

I need to be able to draw a bitmap that is at a specific resolution (~40 DPI), on screen using GDI, and also be able to replicate spacing between each pixel. The space is a fraction of the pixel size, but it is noticeable to the eye.

Is there anyway to setup the Graphics class or a Bitmap to have it insert "white space" between drawn pixels? Before I go after writing the complicated code to do it myself, I'd like to make sure there isn't some setting I'm missing somewhere.

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It sounds like you want to stretch an image from 40 dpi up to the ~110 dpi of a monitor, but rather than expanding the pixels, still only draw 40 pixels per inch and have the rest be white.

I don't know of anything in GDI that does this. Also, it'll look really bad unless you do integer scaling - i.e. exactly one or two white pixels for every pixel in the original bitmap, which will severely limit your options for the final size. You might be able to tweak that a bit by using subpixel rendering (e.g. ClearType), but that'll be even more specialized code (and monitor-specific!) you'll have to write. As it stands now, you're probably going to have to construct a new bitmap pixel-by-pixel.

You can get reasonably close by creating a new bitmap that is 3x3 times the size of your source bitmap, painting it white, and (pseudocode)

foreach(point p in oldBitmap)
{
    // draw a 2x2 box into every 3x3 box
    newbitmap.DrawBox(p.x * 3, p.y * 3, 2, 2, p.Color); 
}
DrawBitmap(target, newbitmap)

You might want to add some single-pixel adjustments to get a nice white border around the edge.

This still leaves 5/9 of your pixels white, meaning you'll have a very washed-out image.

Are you trying to emulate an old display or something?

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – the difference between const and readonly in C#

Apart from the apparent difference of

having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
const's are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled:

in the case of the const value, it is like a find-replace. The value 2 is 'baked into' the AssemblyB's IL. This means that if tomorrow I update I_CONST_VALUE to 20, AssemblyB would still have 2 till I recompile it.
in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB's IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA and all clients do not need to be recompiled.

So if you are confident that the value of the constant won't change, use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention because he pointed this out first. Also I need to plug where I learned this: Effective C# - Bill Wagner

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C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – the difference between const and readonly in C#

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