I'm currently porting a number of custom MFC CStatic-derived controls from GDI+ to Direct2D.
I've noticed when drawing horizontal and vertical lines with a 1 pixel wide stroke that the lines are in fact drawn 2 pixels wide and slightly transparent. The same applies to rectangles and rounded rectangles (diagonal lines seem to be drawn ok). The following code snippet is an example of what I'm trying to do.
D2D1_ROUNDED_RECT TempRect = D2D1::RoundedRect(Rectangle, 4.0F, 4.0F);
CComPtr<ID2D1SolidColorBrush> pTempBrush = NULL;
pRenderTarget->DrawLine(D2D1::Point2F(Rectangle.left, Rectangle.top), D2D1::Point2F(Rectangle.right, Rectangle.top), pTempBrush, 1.0F);
If a specify a 2 pixel stroke then the lines and rectangles are drawn correctly. That is, exactly 2 pixels wide and 100% opaque.
I've tried playing around with the antialiasing mode on the render target, but if I set the render target as follows:
then the lines look terrible as they are all jagged.
Is there any way that I can force lines to have a 1 pixel stroke while in antialiased mode?
I noticed this too. From what I know you can't force it, but you can get around it by adding/subtracting .5 to your positions.
Eg. here is a rectangle:
|RT->DrawRectangle(&D2D1::RectF(3.5f, 3.5f, 75.5f, 65.5f), Brush, 1, NULL);
In DirectX pixel "positions" are at the center of the pixel. For instance, position 0.0f, 0.0f is the exact center of the upper left pixel.
So, if you try to draw a 1 pixel wide line using a rect from (10,3) to (100,4) the rect doesn't align with the pixels. Instead for each X position it covers half of X,3 and X,4. This is why you are seeing the 2 pixel wide line with half transparency.
To solve this subract half a pixel from your coordinates in both directions.