Implement a new dedicated weight painting shader.

Move the weight paint drawing to the fragment shader. The shader
uses a texture that uses the U.coba_weight custom color band, or
an internal color band.

In addition to actual weights, the shader has to display two
alert colors: missing vertex group, and zero weight. The zero
weight alert has to be blended with regular weight colors,
so that a single alert vertex surrounded by weighted ones is
still visible.

Reviewers: campbellbarton, fclem

Differential Revision: https://developer.blender.org/D3675

Compositor: Added Weighted Standard Curve evaluation

Available in RGB Curve node in the compositor and as modifier in the
sequencer. I reshuffled the values of the enum. But a the first commit
is just 1 day old I think that the order is more important than the file
compatibility.

Compositor: Film-like curve

Film-like curves for the RGB Curve node (Compositor) and Curve Modifier
(Sequencer)

Film-like curves originated from Adobe.
"It?s an RGB curve where the tone curve is applied on the largest and smallest value, and then the middle value is adapted to keep a constant hue as defined by RGB-HSL/HSV. In terms of look and saturation increase it?s very similar to a pure RGB curve, more so than a HSL-L curve or HSV-V curve, but some color shift problems are avoided."

Other tools like Natron, Krita and RawTherapee have implemented this curve tone.

Reviewers: brecht, campbellbarton

Reviewed By: brecht

Tags: #compositing, #video_sequencer

Differential Revision: https://developer.blender.org/D3638

Workbench: Support XRay rendering in OpenGL

OpenGL rendering only implemented the deferred renderer. This commit
will add the forward renderer. The forward renderer is used when XRay
mode is enabled

Workbench: hide background option for OpenGL render

When OpenGL renderer is selected the option for background colors are
displayed, but ignored. For now we hide this option as it makes no sense
to have a viewport color option without viewport or render a 'final'
with a theme color.

Workbench: option to change background

Replaced the draw world option with a shading.background_type enum.
Where the user can select Theme, World or a Custom color.

World and theme colors do not always work in workbench. We needed to
have an option what the user could control locally (per viewport).
Especially when using linked data.

I removed the world background drawing from the draw_manager. It was never used as EEVEE and Workbench both override the logic.

Not 100% sure about the naming of Theme, World, Viewport.
In other parts of blender's codebase World is sometimes called Scene.
Will stick to the names that describes its location best.

{F3990139}

Reviewers: fclem, campbellbarton

Reviewed By: fclem

Subscribers: venomgfx

Tags: #bf_blender_2.8

Differential Revision: https://developer.blender.org/D3551

World: Added 'Viewport Display' panel

The Properties->World tab had no Viewport Display panel. The world color
itself was hidden when the 'use_node_tree' was enabled.

Also renamed the World.horizon_color to World.color as it has nothing to
do with the color of the horizon (old BI feature)

Overlay: enable/disable drawing of specific object types.

This patch will allow users to customize what object types will be drawn by the object mode overlay.
It supports: Empties, Lamps, Cameras, Speakers, Armatures and Lightprobes.

It currently does not support Physics objects due to the overlap it has with other objects types.

Also be aware that in pose mode the armature is drawn, but not by the object mode overlay

Reviewers: campbellbarton

Tags: #bf_blender_2.8

Differential Revision: https://developer.blender.org/D3524

Refactor: SHOW->HIDE

HIDE needs less code also in the future, RNA still uses SHOW.

Refactored into a single option

Technical all options are still there for finetuning.