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tips/tricks for drawing color-managed color picker controls?

Jeremy Selan <jeremy...@...>
 

Are you doing this in qt or pyqt?

-- Jeremy


On Mon, Dec 19, 2011 at 2:00 PM, Paul Miller <pa...@...> wrote:
I'm working on a new set of color picker controls that are properly managed with OCIO.

For simple pots I can just transform each color before painting with my toolkit (I'm not going through OGL for these).

But for more complex controls like color spectrums and color-backed alpha spreads, is there anything other than rendering the control (in float) to a temporary buffer, doing the apply on the buffer, then clipping the buffer (color-wise) to the display?

For example, I'm assuming transforming/clipping each point of a gradient is not the same as generating the gradient in float and transforming/clipping each pixel of it independently?
Paul Miller <pa...@...>
 

On 12/19/2011 4:04 PM, Jeremy Selan wrote:
Are you doing this in qt or pyqt?
My UI is Qt. If I can get away with pre-transforming/clipping my colors and then just feeding them to a QGradient, I'd be happy. But I can render everything into a floating-point backing buffer and clip to the screen if I have to.
Jeremy Selan <jeremy...@...>
 

You should not need a floating-point backing buffer.  You can pretransform a lattice of float colors (or per-pixel for 1d gradients), and then clip + convert to a QColor gradient for drawing.

The big subtlety is that if your gradient interpolation space is scene-linear (and you apply a scene-linear to display view transform), the gradient will look terribly non-uniform.   I.e. Artists will hate it.   The workaround is that you essentially want to separate a view transforms 1D + 3D components, where the 3D part of the view transform is applied, but the 1d part is not.  This is what the COLOR_PICKER role is for.

We have pyqt code that is a nice example of this, let me see if I can get permission to post it.

-- Jeremy


On Mon, Dec 19, 2011 at 2:10 PM, Paul Miller <pa...@...> wrote:
On 12/19/2011 4:04 PM, Jeremy Selan wrote:
Are you doing this in qt or pyqt?

My UI is Qt. If I can get away with pre-transforming/clipping my colors and then just feeding them to a QGradient, I'd be happy. But I can render everything into a floating-point backing buffer and clip to the screen if I have to.
Paul Miller <pa...@...>
 

On 12/19/2011 4:27 PM, Jeremy Selan wrote:
You should not need a floating-point backing buffer. You can
pretransform a lattice of float colors (or per-pixel for 1d gradients),
and then clip + convert to a QColor gradient for drawing.

The big subtlety is that if your gradient interpolation space is
scene-linear (and you apply a scene-linear to display view transform),
the gradient will look terribly non-uniform. I.e. Artists will hate
it. The workaround is that you essentially want to separate a view
transforms 1D + 3D components, where the 3D part of the view transform
is applied, but the 1d part is not. This is what the COLOR_PICKER role
is for.

We have pyqt code that is a nice example of this, let me see if I can
get permission to post it.
Ah yes I noticed my gradients were not looking uniform. If you have an example of using the picker role, that would be awesome.
Paul Miller <pa...@...>
 

On 12/19/2011 4:27 PM, Jeremy Selan wrote:
You should not need a floating-point backing buffer. You can
pretransform a lattice of float colors (or per-pixel for 1d gradients),
and then clip + convert to a QColor gradient for drawing.

The big subtlety is that if your gradient interpolation space is
scene-linear (and you apply a scene-linear to display view transform),
the gradient will look terribly non-uniform. I.e. Artists will hate
it. The workaround is that you essentially want to separate a view
transforms 1D + 3D components, where the 3D part of the view transform
is applied, but the 1d part is not. This is what the COLOR_PICKER role
is for.

We have pyqt code that is a nice example of this, let me see if I can
get permission to post it.
Jeremy - any luck getting some sample code that shows how to avoid the extra display transform?

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