CODEWITHSUNDEEP
c++graphdirect2dlineargradientbrush
user2906294
user2906294

Reputation: 11

Direct2D Drawing with DirectX11: Aligning rectangles on a display graph

I'm working on a graphical application in C++ using Direct2d (DirectX11). The application takes in sensor data and displays the input using rectangles that are placed side-by-side across the x-axis (which represents time). Each rectangle is filled with a linear gradient brush that represents multiple sensor readings at the discrete time interval displayed along the y-axis. When a reading is acquired, the placement for the starting 'x' position of the next rectangle should be exactly where the last one finished i.e. rect1.right should be rect2.left. The start point for each rect is calculated using the pseudocode below:

//find the number of rectangles needed to represent the time scale (rects must be an integer, as we cannot display partial rectangles
int nNumXRects = fAxisLength/fTimeDivision;

//calculate the X-axis increment for each rectangle
float fXIncrement = fXAxisLineLength/(float)NumXRects;

//Get the next x position
rect2.left = rect1.right;
rect2.right = rect2.left + fXIncrement;

My problem is that the graph only appears correctly when the value of fXIncrement is exactly a whole number e.g. 3.0f. This obviously restricts the length of the X-Axis to figures that are multiples of the number of rectangles, times the length of each rectangle. This affects the area available to all the other elements of the application. If the value of the increment is anything other that a whole number, small black lines appear between the rectangles which destroys the appearance and makes the data much harder to interpret. I realise why this is happening in principle - we cannot display a fraction of a pixel for instance, but how should this be done properly so that the rectangles will always match up exactly, regardless of the length of the axis? It would seem that Direct2D is perfect for this and should intrinsically cope with mapping fractional values to physical pixels exactly, but I don't know what the correct approach is beyond by current simplistic solution which is to keep the length of the x-axis fixed (meaning I cannot scale properly and other elements do not have enough space in the horizontal).

Any pointers in the right direction would be much appreciated!

Upvotes: 1

Views: 230

Answers (1)

CodeIT
CodeIT

Reputation: 91

Can't this be fixed by setting the appropriate anti alias mode when drawing the rectangles?

pRenderTarget->SetAntialiasMode(D2D1_ANTIALIAS_MODE_ALIASED);

Upvotes: 1

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