Linear gradient painting is implemented in the following way:
1. The rectangle is divided into segments where each segment represents
a simple linear gradient between an adjacent pair of stops.
2. Each quad is filled separately using a fragment shader that
interpolates between two colors.
For now `angle` and `repeat_length` parameters are ignored.
With these changes it is now possible to create OpenGL context on macOS
and run GPU-painter. For now only QT client has a CLI param that turns
it on though.
Framebuffer object is allocated using OpenGL's API and is not platform
specific which means it could be used on both macOS and Linux unlike
EGL specific PBuffer.
Before, we were using a feature of OpenGL that allows specifying a
pointer to allocated vertex data without creating VBO and VAO, but as
I found out, it does not work on macOS.
This change introduces GL.h with error check wrappers for all the
OpenGL functions we used so far.
For now, the error check is simply:
`VERIFY(glGetError() == GL_NO_ERROR);`
but that is better than continuing execution after encounting an error.
Text painting operates in two steps:
1. Preparation of a texture that contains all the glyphs required for
text painting, along with metadata that describes the locations of
those glyphs within texture beforehand.
2. Blitting glyphs from the prepared texture onto corresponding glyph
quads.
Users of LibAccelGfx will need to call `prepare_glyphs_texture()`,
passing a set of all unique (font, code_paint) pairs, before painting
any text.
In the upcoming changes, Painter will be used to store the state of
OpenGL context. For example, if Painter is aware of the shader that
have already been loaded, it will be possible to reuse them across
repaints. Also, it would be possible to manage state of loaded textures
and add/remove them depending on which ones are present in the next
sequence of painting commands.
This change introduces a new 2D graphics library that uses OpenGL to
perform painting operations. For now, it has extremely limited
functionality and supports only rectangle painting, but we have to
start somewhere.
Since this library is intended to be used by LibWeb, where the
WebContent process does not have an associated window, painting occurs
in an offscreen buffer created using EGL.
For now it is only possible to compile this library on linux.
Offscreen context creation on SerenityOS and MacOS will have to be
implemented separately in the future.
Co-Authored-By: Andreas Kling <awesomekling@gmail.com>
