Here is my predicament. I am trying to draw a multitude of dots that leave trails behind them real time. Heres the difficulty, that line fades. Each dot line has a defined z position and the goal would be for everything to blend properly, in real time.
I am currently doing this geometry with a series of triangles that form a triangle strip (I am not using a triangle strip due to the edge case in the circle buffer and spacial locality). This strip is currently implemented as a sort of circle buffer where old triangles are overridden. Each vertice gets passed in the time it was created and thus it knows how to fade (make transparent) its own color.
To make things more complicated I am also drawing caps on the ends of the dot so there is essentially a half rectangle at the end with fragments of it discarded to shape it into a circle.
All of this presents a predicament for alpha testing as alpha testing requires drawing to be sorted in order of depth. Just about all the geometry is transparent in some form. Even if I can get the triangle strip to do this properly getting the half circle working would be quite difficult.
I set the z position based on the dot's id and use the same value that is used to dim the dot's trail to get the triangle strip to have non-conflicting depth.
As for the half circle part does this mean I am going to have to do two draw calls per circle? One to render their segment of the triangle buffer and the other to draw the semi-circle?
Currently I am using the following memory layout:
const int MAX_INDEX = 200; const int MAX_DOTS = 10000; int bufferIndex = (bufferIndex + 1) % MAX_INDEX; int dotIndex = 0..<MAX_DOTS Rect = triangleStripBuffer[bufferIndex * MAX_DOTS + dotIndex];
You can see that data in there is not naturally sorted by anything other than time but even that cycles and there is no consideration for drawing order.
So I suppose I really need ideas on how I can get the geometry to draw in order so that alpha testing can occur. How do I combine these two different drawing goals in a good way? Do I need to k
I figure this problem is fairly platform agnostic but if it is not I am working with Metal and eventually Vulcan on this.