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(cherry picked from commit ad722d98127144e0ff34523f210247a92f8dbb20)

Raycaster is based on the technique described in "Local Ambient Occlusion
in Direct Volume Rendering" by F. Hernell, P. Ljung, A. Ynnermann in IEEE
TVCG 2010.
Implementation does not allow for precomputed LAO volumes but instead
estimates the LAO term per sample.

This reverts commit e7e55015.

# Conflicts:
#	core/glsl/tools/shading.frag

* gradient computation now properly accounts for anisotropic voxels
* Shaders that fail to compile at startup result in an error on the console, with the option to retry computation (after editing the shader) instead of crashing campvis completely

* OpenGL core context is instantiated and enforced, for better forward compat
* Fixed DLL deployment to RelWithDebInfo and MinSizeRel configurations
* Bumped GLEW to 2.0.0
* Fixed wrong shading in various raycasters (normal was wrong sign)

Squashed commit of the following:

commit 21b33709371459552aff972124e9da4ae0077cf4
Author: Jakob Weiss <jakob.weiss@tum.de>
Date:   Mon Feb 6 15:21:12 2017 +0100

    Fixed number of texture unit query

commit 6592f366c7f24822a8681401cf5a415a622e5f6e
Author: Jakob Weiss <jakob.weiss@tum.de>
Date:   Mon Feb 6 14:27:36 2017 +0100

    Fixed core profile requirements

    * now using Framebuffer ARB version instead of EXT
    * fixed extension handling and windows version recognition
    * Removed pixel transfer functions usage and some validity checks for vis pipelines

commit 36c82733434e63309d092bf85f78f471b56bebfb
Author: Jakob Weiss <jakob.weiss@tum.de>
Date:   Mon Feb 6 13:50:08 2017 +0100

    Bumped glew to 2.0.0

commit 4a4a1d51756aad0e19aef9e723e1dfe7d07a797d
Author: Jakob Weiss <jakob.weiss@tum.de>
Date:   Fri Feb 3 16:26:07 2017 +0100

    First Progress - WIP

# Conflicts:
#	ext/cgt/texturemanager.cpp

* Light sources now have an additional camera input. If this is set, the light source position is relative to the camera coordinate system
* ImageMappingInformation and Texture3D now supply an additional pair of matrices: textureToWorldMatrixInvTransp to transform normals between world and texture space

* glImageResampler now sets the mapping information correctly
* ImageData now asserts that an associated imagemappinginformation has the
  same dimensionality

* texturemanager documentation and parameter fix
* imagerepresetation conversion fix for channel number mismatch

* AbstractPipeline now does explicit GPU timing, implying a Flush of the OpenGL pieline after every processor
* OptionProperty has an extended constructor directly using initializer lists of GenericOption<>'s
* ImageMappingInformation has somehow extended / more complete interface allowing copies and default construction

* Added .editorconfig
* cgt::Texture::downloadTextureToBuffer now does a glFlush() before downloading
* ColorPropertyWidget now supports transparent colors properly

* minor whitespace fix in mainwindow.cpp

* datacontainerinspector can now display alpha-channel only in a meaningful way
* new method in stringutils to display bytes in a humanly readable form
* depth darkening has slightly increased range for lambda
* satisfied formatting OCD

* CSHelper ns contains methods to simplify boilerplate code
* some changes to the cgt::Texture interface
* Shader code now dumped to console when compilation fails (could still use some reworking, i.e. like line numbers)
* updated MedianFilter code

* Adapted cgt::Shader to be able to represent and store CS objects
* cgt::ImageUnit manages the GPU image units in use
* GpuCapabilities has been updated for some related queries
* GLTextureFormatTraits simplify lookup of relevant info for a known internalFormat of a texture

* increased overall font size
* introduced debugging diagnostic to detect when derived processors do not call AbstractProcessor::[de]init()
* fixed processors not adhering to this
* fixed some tab vs spaces problems

* Debug Feature: Thread names for pipelines and some important active threads show in debugger
* fullscreen can be toggled per pipeline via the pipeline property and via ALT+Return key combination

* MultiIndexedGeometry index type is now 32 bit to allow for larger meshes
* MultiIndexedGeometry::generateVertexNormals() can now automatically generate normals for a GL_TRIANGLES topology

Instance names to (re-)name processor instances individually for UI and discrimination of different instances

# Conflicts:
#	core/pipeline/abstractprocessor.h

The ProxyGeometryGenerator now correctly generates oriented geometry for
volumes with arbitrary poses by directly using the TextureToWorld matrix
to transform the bounding box instead of just transforming the bounds.

The background decorator can now blend a texture as well as the color gradient. Currently, at fragments where the texture is (0,0,0,0), it will still use the gradient. Also fixes ProcessorDecoratorBackground::addProperties which did not override AbstractProcessorDecorator::addProperties before due to signature mismatch.

It is now possible to backup and restore 1D transfer functions in a very simple text file format.

Very crude demonstration, mainly to prove that everything compiles and (probably?) works as intended. No writable image representations, hence the weird loopholes to remove the representations from the representations list. No deadlocks! yaay!

Only minimum necessary changes to get image representations to work, no real writable representations.

Access to data entries is now managed through two facilities: DataHandles manage metadata and reference counting to handle memory deallocation properly. ScopedTypedData has been extended to manage threadsafe read/write access to the underlying data.

* Disabled LOD-based gradients since their effect is somewhat questionable, they slow down the rendering and lead to artifacts in some case.
* Removed LOD option from ProcessorDecoratorGradient
* Added OpenGL and GLSL versions up to 4.5 to cgt::GpuCapabilities

Further work on IpsviRaycaster processor. Projection of light direction seems to work now. First step to introduce extra ray integration step at IC lookup. Results are still mixed though.

Fixed invalidation handling in MhdImageWriter processor. Updated campvis Lua bindings to support image access (added bindings for ImageData and ImageRepresentationLocal).

* Fixed deadlock in VolumeRenderer when changing the RaycastingProcessor
* Fixed compile error in ITK module
* Fixed some gcc warnings
* Fixed usage of deprecated ScopedSynchronousGlJobExecution in mainwindow.cpp