EGLImage & Direct Texture

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Overview

EGLImage的存在是为了更方便地在EGL client API之间共享2D Image Data. 那什么是EGL client API呢？OpenGL, OpenGL ES, OpenVG都是EGL client API. EGLImage与下面3个EGL Extensions有关:

  • EGL_KHR_image
  • EGL_KHR_image_base
  • EGL_KHR_image_pixmap

后两个扩展其实是从第一个开离出来的。涉及EGLImage新增的Token和API都是在后两个扩展里定义的。

EGL_KHR_image_base

它定义了一个新的Opaque类型EGLImageKHR

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typedef void * EGLImageKHR;

两者它定义了2个新API

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EGLImageKHR eglCreateImageKHR(
EGLDisplay dpy,
EGLContext ctx,
EGLenum target,
EGLClientBuffer buffer,
const EGLint *attrib_list
);

EGLBoolean eglDestroyImageKHR(
EGLDisplay dpy,
EGLImageKHR image
);

其中，EGLClientBuffer也是Opaque类型

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typedef void * EGLClientBuffer;
  • eglCreateImageKHR() 接受的 targets:
target Notes
EGL_GL_TEXTURE_2D Used for GL 2D texture images
EGL_GL_TEXTURE_CUBE_MAP_POSITIVE_X Used for the +X face of GL cubemap texture images
EGL_GL_TEXTURE_CUBE_MAP_NEGATIVE_X Used for the -X face of GL cubemap texture images
EGL_GL_TEXTURE_CUBE_MAP_POSITIVE_Y Used for the +Y face of GL cubemap texture images
EGL_GL_TEXTURE_CUBE_MAP_NEGATIVE_Y Used for the -Y face of GL cubemap texture images
EGL_GL_TEXTURE_CUBE_MAP_POSITIVE_Z Used for the +Z face of GL cubemap texture images
EGL_GL_TEXTURE_CUBE_MAP_NEGATIVE_Z Used for the -Z face of GL cubemap texture images
EGL_GL_TEXTURE_3D Used for GL 3D texture images
EGL_GL_RENDERBUFFER Used for GL renderbuffer images
EGL_NATIVE_PIXMAP_KHR Used for X11 Pixmap (added EGL_KHR_image_pixmap)
  • eglCreateImageKHR() 接受的 attributes:
attribute Notes
EGL_WIDTH
EGL_HEIGHT
EGL_LINUX_DRM_FOURCC_EXT
EGL_DMA_BUF_PLANE0_FD_EXT 0x3272
EGL_DMA_BUF_PLANE0_OFFSET_EXT 0x3273
EGL_DMA_BUF_PLANE0_PITCH_EXT 0x3274
EGL_DMA_BUF_PLANE1_FD_EXT 0x3275
EGL_DMA_BUF_PLANE1_OFFSET_EXT 0x3276
EGL_DMA_BUF_PLANE1_PITCH_EXT 0x3277
EGL_DMA_BUF_PLANE2_FD_EXT 0x3278
EGL_DMA_BUF_PLANE2_OFFSET_EXT 0x3279
EGL_DMA_BUF_PLANE2_PITCH_EXT 0x327A

EGLImageKHR in kylin-wlcom

sequenceDiagram
    autonumber

    participant app
    participant compositor
    participant libwlroots
    participant mesa
    participant kernel

    app ->> compositor : REQUEST:create_prime_buffer <- fd
    compositor -->> compositor : drm_handle_create_prime_buffer(..., fd, ...)
    compositor ->> libwlroots  : wlr_buffer_init(..., &buffer_impl, ...)
    compositor -->> compositor : API:buffer_get_dmabuf(struct wlr_buffer *, struct wlr_dmabuf_attributes *)
    compositor ->> libwlroots  : wlr_buffer_get_dmabuf(struct wlr_buffer *, struct wlr_dmabuf_attributes *)
    compositor -->> compositor : gl_texture_from_dmabuf_buffer()
    compositor -->> compositor : gl_texture_from_dmabuf()
    compositor -->> compositor : ky_egl_create_image_from_dmabuf() -> EGLImageKHR
    compositor ->> mesa        : eglCreateImageKHR() -> EGLImageKHR
    mesa -->> mesa : dri2_create_image()
    mesa -->> mesa : dri2_create_image_dma_buf()
    mesa -->> mesa : ???_resource_from_handle()
    mesa -->> mesa : ???_bo_import(..., fd) 
    mesa ->> kernel: drmPrimeFDToHandle(..., fd) -> gem_handle

EGL_KHR_image_pixmap