20 Jun
2010
20 Jun
'10
6:59 a.m.
On Fri, Jun 18, 2010 at 1:10 PM, Johannes Kroll <jkroll(a)lavabit.com> wrote:
On Thu, 17 Jun 2010 00:29:44 -0400
Jeremy <jeremybubs(a)gmail.com> wrote:
I used a setpixel function, but it was quite simply a pointer dereferencer.
I believe I am doing exactly what you are suggesting, but with SDL.
Writing directly to the array, and then calling flip. I think I realize
why I'm having this problem. I'm using moderately old hardware, which
doesn't have any linux acceleration driver (even 2d), so everything is
written to main memory and then copied on flip (I believe). This is why
it's slow. Even with this, I only get xruns when I click another window, or
try to drag or resize a window. Basically, it's good enough that if I put
the flip() call in another thread it probably should run perfectly.
Jeremy
Hi,
When I'm programming, I find it immensely helpful to be able to plot
audio
data at different points in its processing, for
debugging, and to test
new
ideas.
Essentially I want an oscilloscope, which plots each chunk of 1024
samples.
I've tried using libplot, but it seems too slow. It's causing constant
xruns, even when I only plot every 5th sample.
I thought that maybe libplot was too abstract, and that I needed to draw
the
pixels on the screen directly. I tried using
SDL, but it caused
excessive
xruns also. Simply setting 48000 pixels per
second was enough to cause
the
flow of xruns. This is *not* erasing the
screen, just drawing the
points.
I'd expect that erasing the screen is the
slow part, but apparently not.
How did you write your SDL program? Don't use any Setpixel functions.
Draw your pixels to a memory buffer/surface with the same pixel format
as the screen and flip that to the screen. Or try OpenGL. Use GL Arrays
if glBegin()/glEnd() is too slow.
The hardware shouldn't be a bottleneck if you don't use a system
older than 10 years or so. If you use OpenGL, you need an accelerated
driver of course, else it's useless.
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