Starboard Module Reference: decode_target.h

A target for decoding image and video data into. This corresponds roughly to an EGLImage, but that extension may not be fully supported on all GL platforms. SbDecodeTarget supports multi-plane targets. The SbBlitter API is supported as well, and this is able to more-or-less unify the two.

An SbDecodeTarget can be passed into any function which decodes video or image data. This allows the application to allocate fast graphics memory, and have decoding done directly into this memory, avoiding unnecessary memory copies, and also avoiding pushing data between CPU and GPU memory unnecessarily.

SbDecodeTargetFormat

SbDecodeTargets support several different formats that can be used to decode into and render from. Some formats may be easier to decode into, and others may be easier to render. Some may take less memory. Each decoder needs to support the SbDecodeTargetFormat passed into it, or the decode will produce an error. Each decoder provides a way to check if a given SbDecodeTargetFormat is supported by that decoder.

SbDecodeTargetGraphicsContextProvider

Some components may need to acquire SbDecodeTargets compatible with a certain rendering context, which may need to be created on a particular thread. The SbDecodeTargetGraphicsContextProvider are passed in to the Starboard implementation from the application and provide information about the rendering context that will be used to render the SbDecodeTarget objects. For GLES renderers, it also provides functionality to enable the Starboard implementation to run arbitrary code on the application's renderer thread with the renderer's EGLContext held current. This may be useful if your SbDecodeTarget creation code needs to execute GLES commands like, for example, glGenTextures().

The primary usage is likely to be the the SbPlayer implementation on some platforms.

SbDecodeTarget Example

Let's say that we are an application and we would like to use the interface defined in starboard/image.h to decode an imaginary "image/foo" image type.

First, the application should enumerate which SbDecodeTargetFormats are supported by that decoder.

SbDecodeTargetFormat kPreferredFormats[] = {
    kSbDecodeTargetFormat3PlaneYUVI420,
    kSbDecodeTargetFormat1PlaneRGBA,
    kSbDecodeTargetFormat1PlaneBGRA,
};

SbDecodeTargetFormat format = kSbDecodeTargetFormatInvalid;
for (int i = 0; i < SB_ARRAY_SIZE_INT(kPreferredFormats); ++i) {
  if (SbImageIsDecodeSupported("image/foo", kPreferredFormats[i])) {
    format = kPreferredFormats[i];
    break;
  }
}

Now that the application has a format, it can create a decode target that it will use to decode the .foo file into. Let's assume format is kSbDecodeTargetFormat1PlaneRGBA, that we are on an EGL/GLES2 platform. Also, we won't do any error checking, to keep things even simpler.

SbDecodeTarget target = SbImageDecode(
    context_provider, encoded_foo_data, encoded_foo_data_size,
    "image/foo", format);

// If the decode works, you can get the texture out and render it.
SbDecodeTargetInfo info;
SbMemorySet(&info, 0, sizeof(info));
SbDecodeTargetGetInfo(target, &info);
GLuint texture =
    info.planes[kSbDecodeTargetPlaneRGBA].texture;

Macros

kSbDecodeTargetInvalid

Well-defined value for an invalid decode target handle.

Enums

SbDecodeTargetFormat

The list of all possible decoder target formats. An SbDecodeTarget consists of one or more planes of data, each plane corresponding with a surface. For some formats, different planes will be different sizes for the same dimensions.

NOTE: For enumeration entries with an alpha component, the alpha will always be premultiplied unless otherwise explicitly specified.

Values

  • kSbDecodeTargetFormat1PlaneRGBA

    A decoder target format consisting of a single RGBA plane, in that channel order.

  • kSbDecodeTargetFormat1PlaneBGRA

    A decoder target format consisting of a single BGRA plane, in that channel order.

  • kSbDecodeTargetFormat2PlaneYUVNV12

    A decoder target format consisting of Y and interleaved UV planes, in that plane and channel order.

  • kSbDecodeTargetFormat3PlaneYUVI420

    A decoder target format consisting of Y, U, and V planes, in that order.

  • kSbDecodeTargetFormat3Plane10BitYUVI420

    A decoder target format consisting of 10bit Y, U, and V planes, in that order.

  • kSbDecodeTargetFormat1PlaneUYVY

    A decoder target format consisting of a single plane with pixels layed out in the format UYVY. Since there are two Y values per sample, but only one U value and only one V value, horizontally the Y resolution is twice the size of both the U and V resolutions. Vertically, they Y, U and V all have the same resolution. This is a YUV 422 format. When using this format with GL platforms, it is expected that the underlying texture will be set to the GL_RGBA format, and the width of the texture will be equal to the number of UYVY tuples per row (e.g. the u/v width resolution). Content region left/right should be specified in u/v width resolution.

  • kSbDecodeTargetFormatInvalid

    An invalid decode target format.

SbDecodeTargetPlane

All the planes supported by SbDecodeTarget.

Values

  • kSbDecodeTargetPlaneRGBA

    The RGBA plane for the RGBA format.

  • kSbDecodeTargetPlaneBGRA

    The BGRA plane for the BGRA format.

  • kSbDecodeTargetPlaneY

    The Y plane for multi-plane YUV formats.

  • kSbDecodeTargetPlaneUV

    The UV plane for 2-plane YUV formats.

  • kSbDecodeTargetPlaneU

    The U plane for 3-plane YUV formats.

  • kSbDecodeTargetPlaneV

    The V plane for 3-plane YUV formats.

Typedefs

SbDecodeTarget

A handle to a target for image data decoding.

Definition

typedef SbDecodeTargetPrivate* SbDecodeTarget

SbDecodeTargetGlesContextRunner

Signature for a function provided by the application to the Starboard implementation that will let the Starboard implementation run arbitrary code on the application's renderer thread with the application's EGLContext held current.

Definition

typedef void(* SbDecodeTargetGlesContextRunner) (struct SbDecodeTargetGraphicsContextProvider *graphics_context_provider, SbDecodeTargetGlesContextRunnerTarget target_function, void *target_function_context)

SbDecodeTargetGlesContextRunnerTarget

Signature for a Starboard implementaion function that is to be run by a SbDecodeTargetGlesContextRunner callback.

Definition

typedef void(* SbDecodeTargetGlesContextRunnerTarget) (void *gles_context_runner_target_context)

Structs

SbDecodeTargetGraphicsContextProvider

In general, the SbDecodeTargetGraphicsContextProvider structure provides information about the graphics context that will be used to render SbDecodeTargets. Some Starboard implementations may need to have references to some graphics objects when creating/destroying resources used by SbDecodeTarget. References to SbDecodeTargetGraphicsContextProvider objects should be provided to all Starboard functions that might create SbDecodeTargets (e.g. SbImageDecode()).

Members

  • SbBlitterDevice device

    The SbBlitterDevice object that will be used to render any produced SbDecodeTargets.

SbDecodeTargetInfo

Contains all information about a decode target, including all of its planes. This can be queried via calls to SbDecodeTargetGetInfo().

Members

  • SbDecodeTargetFormat format

    The decode target format, which would dictate how many planes can be expected in planes.

  • bool is_opaque

    Specifies whether the decode target is opaque. The underlying source of this value is expected to be properly maintained by the Starboard implementation. So, for example, if an opaque only image type were decoded into an SbDecodeTarget, then the implementation would configure things in such a way that this value is set to true. By opaque, it is meant that all alpha values are guaranteed to be 255, if the decode target is of a format that has alpha values. If the decode target is of a format that does not have alpha values, then this value should be set to true. Applications may rely on this value in order to implement certain optimizations such as occlusion culling.

  • int width

    The width of the image represented by this decode target.

  • int height

    The height of the image represented by this decode target.

  • SbDecodeTargetInfoPlane planes

    The image planes (e.g. kSbDecodeTargetPlaneRGBA, or {kSbDecodeTargetPlaneY, kSbDecodeTargetPlaneU, kSbDecodeTargetPlaneV} associated with this decode target.

SbDecodeTargetInfoContentRegion

Defines a rectangular content region within a SbDecodeTargetInfoPlane structure.

Members

  • float left

    If the texture (width, height) is set to (1, 1), then these values will be interpreted as normalized coordinates, and depending on the platform (for example GLES 2.0 provides no method of obtaining the texture width/height) this may be more natural than specifying absolute pixel offsets.

  • float top

  • float right

  • float bottom

SbDecodeTargetInfoPlane

Defines an image plane within a SbDecodeTargetInfo object.

Members

  • SbBlitterSurface surface

    A handle to the Blitter surface that can be used for rendering.

  • int width

    The width of the texture/surface for this particular plane.

  • int height

    The height of the texture/surface for this particular plane.

  • SbDecodeTargetInfoContentRegion content_region

    The following properties specify a rectangle indicating a region within the texture/surface that contains valid image data. The top-left corner is (0, 0) and increases to the right and to the bottom. The units specified by these parameters are number of pixels. The range for left/right is [0, width], and for top/bottom it is [0, height].

Functions

PrivateDecodeTargetReleaser

This function is just an implementation detail of SbDecodeTargetReleaseInGlesContext() and should not be called directly.

Declaration

static void PrivateDecodeTargetReleaser(void *context)

SbDecodeTargetGetInfo

Writes all information about decode_target into out_info. Returns false if the provided out_info structure is not zero initialized.

Declaration

bool SbDecodeTargetGetInfo(SbDecodeTarget decode_target, SbDecodeTargetInfo *out_info)

SbDecodeTargetIsFormatValid

Returns whether a given format is valid.

Declaration

static bool SbDecodeTargetIsFormatValid(SbDecodeTargetFormat format)

SbDecodeTargetIsValid

Returns whether the given file handle is valid.

Declaration

static bool SbDecodeTargetIsValid(SbDecodeTarget handle)

SbDecodeTargetRelease

Returns ownership of decode_target to the Starboard implementation. This function will likely result in the destruction of the SbDecodeTarget and all its associated surfaces, though in some cases, platforms may simply adjust a reference count. In the case where SB_HAS(GLES2), this function must be called on a thread with the context

Declaration

void SbDecodeTargetRelease(SbDecodeTarget decode_target)

SbDecodeTargetReleaseInGlesContext

Helper function that is possibly useful to Starboard implementations that will release a decode target on the thread with the GLES context current.

Declaration

static void SbDecodeTargetReleaseInGlesContext(SbDecodeTargetGraphicsContextProvider *provider, SbDecodeTarget decode_target)

SbDecodeTargetRunInGlesContext

Inline convenience function to run an arbitrary SbDecodeTargetGlesContextRunnerTarget function through a SbDecodeTargetGraphicsContextProvider . This is intended to be called by Starboard implementations, if it is necessary.

Declaration

static void SbDecodeTargetRunInGlesContext(SbDecodeTargetGraphicsContextProvider *provider, SbDecodeTargetGlesContextRunnerTarget target, void *target_context)