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Thread: Best way to render a "rectangle matrix"

  1. #1
    Newbie Newbie
    Join Date
    Jul 2013
    Posts
    1

    Question Best way to render a "rectangle matrix"

    Hi

    I'm new to OpenGL programming and I'm working on a 2-d heatmap style animation.
    - got 2-d array of double values (say 800x800 max)
    - points should be represented as "big pixels" (rectangles, color-coded)
    - goal is to display at around 30 FPS

    First, I tried to visualize the array using GDI on Windows. Sure got 3-4 FPS...
    Now trying to render using Qt/OpenGL I build a large amount of rectangles,
    one for every point of the 2-d array. My naive approach with only
    glColor() and glRect() calls works much better (about 20-30 FPS) if the
    array stays small (300x300).

    However, obviously there are smarter ways to do this. So please, give me
    some optimization advice.

    Some things I already thought about:
    - rect grid does not change -> move it to the GPU once (how?), update colors only
    - draw a bitmap texture (CPU pixel-wise access to a bitmap might be even slower
    than drawing thousands of rects on GPU)

    Any suggestions are welcome!
    Thank you.

  2. #2
    Senior Member OpenGL Pro
    Join Date
    Jan 2012
    Location
    Australia
    Posts
    1,101
    rect grid does not change -> move it to the GPU once (how?), update colors only

    This is the right approach but since you are new to OpenGL you should wander your way through this
    http://www.opengl-tutorial.org/ it will answer the how-to

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