Migrating to librashader ABI 2

October 3, 2024 · View on GitHub

librashader version 0.5.0 introduces an ABI change to the C ABI that is incompatible with prior versions.

If a version of librashader prior to 0.5.0 was linked via libashader_ld.h, it should correctly fail to load when attempting to load an instance of librashader 0.5.0 or later.

This document is only relevant to consumers of the librashader C ABI. Rust users should consult docs.rs/librashader.

LIBRASHADER_CURRENT_ABI change

LIBRASHADER_CURRENT_ABI has changed from 1 to 2. There is no change to LIBRASHADER_CURRENT_API, as new features have not been added. Option structs should continue to pass LIBRASHADER_CURRENT_API for the latest available feature set.

SONAME change

On Linux, the canonical SONAME of librashader.so has changed from librashader.so.1 to librashader.so.2. This will affect consumers that link via the linkage table with -lrashader or equivalent rather than through libashader_ld.h.

libra_preset changes

  • The _internal_alloc field from libra_preset_param_list_t has been removed. This change was made to reduce the potential surface area for undefined behaviour to occur. If librashader was used correctly, there is no code change required.

LIBRA_RUNTIME_VULKAN changes

The following changes are applicable if LIBRA_RUNTIME_VULKAN is defined.

  • The libra_output_image_vk_t and libra_source_image_vk_t structs have been replaced with libra_image_vk_t.
    • libra_image_vk_thas the same layout and semantics for libra_source_image_vk_t.
    • When passed as out, you should now pass what was previously .width and .height of libra_viewport_t to the same fields in libra_image_vk_t. The handle and format fields retain the same semantics as libra_output_image_vk_t.
  • A field queue of type VkQueue was added to libra_device_vk_t. This field can be NULL. If not NULL, it is the handle to the VkQueue graphics queue to use for the filter chain. If NULL, a suitable queue will be chosen.
  • The image and out parameters of libra_vk_filter_chain_frame has changed from libra_source_image_vk_t and libra_output_image_vk_t, to libra_image_vk_t.
  • In libra_vk_filter_chain_frame, the position of the viewport parameter has moved to after the out parameter, and its type has changed from libra_viewport_t to libra_viewport_t *, which is allowed to be NULL. See libra_viewport_t changes for more details.
  • The chain parameter of libra_vk_filter_chain_get_param has been made const.
  • It is always thread safe to call libra_vk_filter_chain_set_param from any thread 1.

LIBRA_RUNTIME_OPENGL changes

The following changes are applicable if LIBRA_RUNTIME_OPENGL is defined.

  • The libra_gl_init_context function has been removed.
  • The function libra_gl_filter_chain_create now accepts a loader parameter of type libra_gl_loader_t. This will be the OpenGL loader used to create the filter chain, previously passed to libra_gl_init_context The filter chain will be created against the current OpenGL context.
  • The libra_output_framebuffer_gl_t and libra_source_image_gl_t structs have been replaced with libra_image_gl_t.
    • libra_image_gl_thas the same layout and semantics for libra_source_image_gl_t.
    • When passed as out, you should now pass what was previously .width and .height of libra_viewport_t to the same fields in libra_image_gl_t. The handle and format fields retain the same semantics as libra_output_image_gl_t.
    • The fbo field previously in libra_output_image_gl_t is no longer necessary. librashader will now internally manage a framebuffer object to write to the provided texture.
  • In libra_gl_filter_chain_frame, the position of the viewport parameter has moved to after the out parameter, and its type has changed from libra_viewport_t to libra_viewport_t *, which is allowed to be NULL. See libra_viewport_t changes for more details.
  • The chain parameter of libra_gl_filter_chain_get_param has been made const.
  • It is always thread safe to call libra_gl_filter_chain_set_param from any thread 1.

LIBRA_RUNTIME_D3D11 changes

The following changes are applicable if LIBRA_RUNTIME_D3D11 is defined.

  • The image parameter of libra_d3d11_filter_chain_frame has changed from libra_source_image_d3d11_t to ID3D11ShaderResourceView *.
    • You should now pass what was previously the .handle field of libra_source_image_d3d11_t field directly as image to libra_d3d11_filter_chain_frame.
  • The libra_source_image_d3d11_t struct has been removed.
  • In libra_d3d11_filter_chain_frame, the position of the viewport parameter has moved to after the out parameter, and its type has changed from libra_viewport_t to libra_viewport_t *, which is allowed to be NULL. See libra_viewport_t changes for more details.
  • The chain parameter of libra_d3d11_filter_chain_get_param has been made const.
  • It is always thread safe to call libra_d3d11_filter_chain_set_param from any thread 1.

LIBRA_RUNTIME_D3D12 changes

The following changes are applicable if LIBRA_RUNTIME_D3D12 is defined.

  • The lifetime of resources will not be extended past the call to the libra_d3d12_filter_chain_frame function. In other words, the refcount for any resources passed into the function will no longer be changed, and it is explicitly the responsibility of the caller to ensure any resources remain alive until the ID3D12GraphicsCommandList provided is submitted.
  • The fields format, width, and height have been removed from libra_source_image_d3d12_t.
  • The field descriptor now comes before the field resource in the layout of libra_source_image_d3d12_t.
  • The fields width and height have been added to libra_output_image_d3d12_t.
    • You should now pass what was previously .width and .height of libra_viewport_t to these new fields in libra_output_image_d3d12_t.
  • The image parameter of libra_d3d12_filter_chain_frame has changed from libra_source_image_d3d12_t to libra_image_d3d12_t.
    • To maintain the previous behaviour, .image_type of the libra_image_d3d12_t should be set to LIBRA_D3D12_IMAGE_TYPE_SOURCE_IMAGE, and .handle.source should be the libra_source_image_d3d12_tstruct.
  • The out parameter of libra_d3d12_filter_chain_frame has changed from libra_output_image_d3d11_t to libra_image_d3d12_t.
    • To maintain the previous behaviour, .image_type of the libra_image_d3d12_t should be set to LIBRA_D3D12_IMAGE_TYPE_OUTPUT_IMAGE, and .handle.output should be the libra_output_image_d3d12_tstruct.
  • Any libra_image_d3d12_t can now optionally pass only the ID3D12Resource * for the texture by setting .image_type to LIBRA_D3D12_IMAGE_TYPE_RESOURCE and setting .handle.resource to the resource pointer.
    • If using LIBRA_D3D12_IMAGE_TYPE_RESOURCE, shader resource view and render target view descriptors for the input and output images will be internally allocated by the filter chain. This may result in marginally worse performance.
  • In libra_d3d12_filter_chain_frame, the position of the viewport parameter has moved to after the out parameter, and its type has changed from libra_viewport_t to libra_viewport_t *, which is allowed to be NULL. See libra_viewport_t changes for more details.
  • The chain parameter of libra_d3d12_filter_chain_get_param has been made const.
  • It is always thread safe to call libra_d3d12_filter_chain_set_param from any thread 1.

LIBRA_RUNTIME_D3D9 changes

The following changes are applicable if LIBRA_RUNTIME_D3D9 is defined.

  • In libra_d3d9_filter_chain_frame, the position of the viewport parameter has moved to after the out parameter, and its type has changed from libra_viewport_t to libra_viewport_t *, which is allowed to be NULL. See libra_viewport_t changes for more details.
  • The chain parameter of libra_d3d9_filter_chain_get_param has been made const.
  • It is always thread safe to call libra_d3d9_filter_chain_set_param from any thread 1.

LIBRA_RUNTIME_METAL changes

The following changes are applicable if LIBRA_RUNTIME_METAL is defined.

  • In libra_mtl_filter_chain_frame, the position of the viewport parameter has moved to after the out parameter, and its type has changed from libra_viewport_t to libra_viewport_t *, which is allowed to be NULL. See libra_viewport_t changes for more details.
  • The chain parameter of libra_mtl_filter_chain_get_param has been made const.
  • It is always thread safe to call libra_mtl_filter_chain_set_param from any thread 1.

libra_viewport_t changes

All viewport parameters for libra_*_filter_chain_frame now take a pointer to a libra_viewport_t struct. In ABI 1, the semantics of libra_viewport_t was unspecified (but not undefined behaviour) if width and height did not match the width and height of the output texture.

This caused confusion as to what the actual purpose of the width and height fields were. The behaviour differed across runtimes: In some runtimes, it specified the size of the output texture, in others they were used to set the clipping rect for the render target.

In ABI 2, the semantics of viewport as a parameter in libra_*_filter_chain_frame are as specified.

  • If viewport is NULL, then this will be the same as the specified behaviour in ABI 1—that is, as if the behaviour where width and height of libra_viewport_t were equal to that of the output texture.
    • In other words, if viewport is NULL, then it will set the render viewport to be equal to the width and height of the output texture.
  • If viewport is not NULL, then the following occurs.
    • The width and height of the viewport rectangle for the output quad will be set to viewport.width and viewport.height respectively.
    • The origin point of the viewport rectangle will be set to (x, y), in the native coordinate system of the runtime.
      • This behaviour may change over an API version bump. API version 1 will always retain the behaviour specified here.
    • The scissor rectangle will be set to the same size and origin as the viewport rectangle.

Footnotes

  1. This has been the case since librashader 0.4.0 on ABI 1. ABI 2 codifies this guarantee: any loosening in the thread-safety guarantees of libra_*_filter_chain_set_param in the future may only change across an API version bump. API version 1 will always retain the behaviour specified here. ↩ ↩2 ↩3 ↩4 ↩5 ↩6