Ben Doherty
1c5715824f
Some clients need to link against both Filament and OpenGL. This can lead to symbol clashes under certain circumstances. As a fix, prefix all of our `bluegl` symbols with `bluegl_`. Previously we made this naming change for Windows, but now we'll do it on all platforms for simplicity.
65 lines
1.6 KiB
Markdown
65 lines
1.6 KiB
Markdown
# BlueGL Mechanics
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So you want to call `glClear()`?
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## Step 0: Run `bluegl-gen.py`
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This step is only required if updating or modifying BlueGL. These artifacts should already be checked into the Filament repository.
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From the `libs/bluegl` folder, run:
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```
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./bluegl-gen.py
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```
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The `bluegl-gen.py` script generates a set of files:
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- assembly (proxy) files: `BlueGLCore*.S`
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- header files: `include/BlueGLDefines.h` and `include/bluegl/BlueGL.h`
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- a private header:`include/private_BlueGL.h`
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## Step 1: Include the BlueGL defines header:
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```
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#include <bluegl/BlueGLDefines.h>
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```
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This headers adds a bunch of defines:
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```
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...
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#define glClear bluegl_glClear
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...
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```
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## Step 2: Include the BlueGL header after the defines header:
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```
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#include <bluegl/BlueGLDefines.h>
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#include <bluegl/BlueGL.h>
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```
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This also includes the GL headers, like `<GL/glcorearb.h>` for you.
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## Step 3: Call `bluegl::bind()`
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Internally, the BlueGL library maintains a list of function pointers:
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```
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void* __blue_glCore_glClear;
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```
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During `bluegl::bind()`, each function gets assigned to the appropriate symbol loaded from the OS-specific GL shared library via `dlopen`, `dlsym`, and equivalents.
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## Step 4: Call `glClear()`
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Because of the prior `#define`, you'll actually be calling `bluegl_glClear()`. This is a trampoline function, defined in the `BlueGLCore*.S` assembly file (the exact implementation varies slightly on each platform):
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```
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.private_extern _bluegl_glClear
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_bluegl_glClear:
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mov ___blue_glCore_glClear@GOTPCREL(%rip), %r11
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jmp *(%r11)
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```
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The invokes the `__blue_glCore_glClear` function, which was previously assigned to the actual GL function.
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