Plotting into buffer

Specific Domains Visualization
,
1

Is it possible and how to plot into an existing buffer with Makie.jl ? My guess is that Cairomakie.jl would be the choice, but I can’t find a solution for it.

The reason for this task is, that I want to hand over the buffer to a C library several times.

Here is an example for a 3D plot (from gallery Beautiful Makie) without the buffer:

using ImageView
using CairoMakie

CairoMakie.activate!()
x = -2:0.005:2
y = -2:0.005:2
f(z) = (z^2 + 1) / (z^2 - 1)
fvals = [f(u + 1im * v) for u in x, v in y]
fvalues = abs.(fvals)
fargs = angle.(fvals)
indxCut = fvalues .> 3
fvalues[indxCut] .= 3.01
fig, ax, pltobj = surface(x, y, fvalues, color = fargs,
    colormap = :roma, colorrange = (-π, π),
    backlight = 1.0f0, highclip = :black,
    figure = (; size = (800, 600), fontsize = 22));
display(fig)
imshow(colorbuffer(fig.scene))

Here is some pseudocode for what I want to do

using CairoMakie

CairoMakie.activate!()

buffer=zeros(RGB24, 800, 600)

function draw_into_buffer!(buffer)
	x = -2:0.005:2
	y = -2:0.005:2
	f(z) = (z^2 + 1) / (z^2 - 1)
	fvals = [f(u + 1im * v) for u in x, v in y]
	fvalues = abs.(fvals)
	fargs = angle.(fvals)
	indxCut = fvalues .> 3
	fvalues[indxCut] .= 3.01

	#PSEUDOCODE: plot into existing buffer:
	surface_into_buffer(buffer, x, y, fvalues, color = fargs,
		colormap = :roma, colorrange = (-π, π),
		backlight = 1.0f0, highclip = :black,
		figure = (; size = (1200, 800), fontsize = 22));
end

draw_into_buffer!(buffer);

#provide buffer to some C library as pointer(buffer)

How can I tell CairoMakie to plot into an existing buffer for image pixels?

The prefered idea is not to copy again and again from colorbuffer(fig.scene) to buffer for performance.

2

You have to go a bit into internals but you can construct a CairoScreen from a CairoARGBSurface that is backed by an array that you create. But the memory layout must be the same.

I can’t send an example now but will try it out in a bit.

1 Like
3

Thanks a lot, I am waiting for it… I see the idea already but for today I can’t go into my own experiments…

4 
using CairoMakie
using CairoMakie.Colors

sz = (400, 300)
px_per_unit = 2
img = fill(ARGB32(1, 0, 0, 1), ((sz .* px_per_unit) .+ (200, 0))...)
surf = CairoMakie.Cairo.CairoImageSurface(img)

f = Figure(size = sz)
scatter(f[1, 1], cumsum(randn(100)))

conf = Makie.merge_screen_config(CairoMakie.ScreenConfig, Dict(:px_per_unit => px_per_unit))
scr = CairoMakie.Screen(f.scene, conf, surf)
CairoMakie.cairo_draw(scr, f.scene)

save("test.png", img')

test
test1000×600 4.13 KB

The red section on the side is just to visualize that I mutated the original array filled with red

3 Likes
5

Thanks for the code.

Yet I am still not happy because the line CairoMakie.cairo_draw(scr, f.scene) is so slow, that it doesn’t work very good in my interactive scenario.
The code I tried now is:

using CairoMakie
using CairoMakie.Colors

buffer = zeros(UInt32, 800, 600)

function draw()
	amplitude = 5.0
	sz = (800, 600)
	px_per_unit = 1
	surf = CairoMakie.Cairo.CairoImageSurface(buffer, CairoMakie.Cairo.FORMAT_ARGB32; flipxy=false)
	conf = Makie.merge_screen_config(CairoMakie.ScreenConfig, Dict(:px_per_unit => px_per_unit))

	x = -2:0.005:2
	y = -2:0.005:2
	f(z) = (amplitude/5.0) * (z^2 + 1) / (z^2 - 1)
	fvals = [f(u + 1im * v) for u in x, v in y]
	fvalues = abs.(fvals)
	fargs = angle.(fvals)
	indxCut = fvalues .> 3
	fvalues[indxCut] .= 3.01
	fig, ax, pltobj = surface(x, y, fvalues, color = fargs,
		colormap = :roma, colorrange = (-π, π),
		backlight = 1.0f0, highclip = :black,
		figure = (; size = sz, fontsize = 22));

	resize_to_layout!(fig)
	scr = CairoMakie.Screen(fig.scene, conf, surf)
	CairoMakie.cairo_draw(scr, fig.scene)
end
draw()

The last line in the draw() function, CairoMakie.cairo_draw(scr, fig.scene), uses several seconds, which makes interactivity very annoying.

In general it is working quite well: the buffer can be passed to the C library and it shows up correctly.

Perhaps CairoMakie wasn’t the best choice for a Julia plotting library to plot a 3d function into an existing buffer. What I additionally need is fast rendering into the buffer.

Any suggestions?

6

Ah yeah that’s because 3D mesh drawing is the weak point in Cairo, and you’re doing a fairly detailed surface with 640k vertices. Not sure if @sdanisch has a good idea how to do this with GLMakie. But the buffer would be on the GPU there, so a copy would have to be made, whether into an existing buffer or as a separate array like colorbuffer does it. I don’t think OpenGL would draw directly into a RAM buffer.

1 Like
7

In GLMakie we already draw in a pre-allocated frame cache, which I guess you could just use?

1 Like
8

Thanks, will try…

9

Something is not as expected.
The plot renders nicely but the framecache is not the full picture:

using GLMakie
using GLMakie.Colors

amplitude = 5.0
sz = (800, 600)
px_per_unit = 1

x = -2:0.005:2
y = -2:0.005:2
f(z) = (amplitude/5.0) * (z^2 + 1) / (z^2 - 1)
fvals = [f(u + 1im * v) for u in x, v in y]
fvalues = abs.(fvals)
fargs = angle.(fvals)
indxCut = fvalues .> 3
fvalues[indxCut] .= 3.01
fig, ax, pltobj = surface(x, y, fvalues, color = fargs,
	colormap = :roma, colorrange = (-π, π),
	backlight = 1.0f0, highclip = :black,
	figure = (; size = sz, fontsize = 22));

resize_to_layout!(fig)

scr = GLMakie.Screen(fig.scene);

julia> scr.framecache
10×10 Matrix{RGB{FixedPointNumbers.N0f8}}:
 RGB(0.004, 0.0, 0.0)  RGB(0.0, 0.0, 0.02)   RGB(0.0, 0.0, 0.0) ...
...

Perhaps scr.framebuffer can be used, but it’s a more complex structure so I can’t see how?

For those late in the thread:
How to repeatedly plot (e.g. a nice 3D function) directly into a (predefined) buffer with good performance without displaying the plot? The raw buffer is repeatedly passed to a C library.

10

It only gets filled when calling colorbuffer(screen) .
You can call that or exctract the relevant bits from the linked source!

1 Like
11

Thanks for all your efforts, but I have trouble doing what I want with Makie:

CairoMakie: CairoMakie.cairo_draw needs several seconds => bad interactivity.

GLMakie: colorbuffer and GLMakie.Screen stalls, probably because the C GUI library uses OpenGL too.

WGLMakie: can’t get the pixel buffer without showing the plot, a browser screen must be open.