Hardware Drawing Capabilities
Some renderers can draw directly to video hardware as they decompress video
frames. These renderers return the VIDCF_DRAW flag in response to the ICGetInfo
function. When using this type of renderer, your application does not have to
handle the decompressed data. It lets the renderer retain the decompressed
data for drawing.
If your application uses a renderer with drawing capabilities, it must handle
the following tasks:
- Select a renderer.
- Specify image formats.
- Initialize the renderer.
- Draw the data.
- Control drawing parameters.
macro opens a renderer that can draw images with the specified format. It
returns a handle of a renderer if it is successful, or zero otherwise. This macro
uses the ICLocate
function to open the renderer.
Specifying Image Formats
Because your application does not need to draw the decompressed data, it does
not require a specific output format. It must, however, ensure that the
renderer can draw using the input format by using the ICM_DRAW_QUERY
message (or use the ICDrawQuery
macro). This message cannot determine if a renderer can draw a bitmap. If
your application must determine if the renderer can draw the bitmap, use this
message with the ICDrawBegin
Your application can have a renderer suggest an input format by using the ICDrawSuggestFormat
function. This function is used when a renderer separates the drawing
capabilities from the decompressing capabilities. Most applications using the drawing
functions will not need to determine the output format.
function initializes a renderer and tells it the drawing destination. This
function can also perform the following tasks:
- Determine whether the renderer supports a specific input format.
- Specify whether the drawing operation occupies a window or the entire screen.
- Specify the part of the image to display using the source rectangle.
- Define the playback rate of the image sequence.
Some renderers buffer the compressed data to operate more efficiently. Your
application can send the ICM_GETBUFFERSWANTED
message (or use the ICGetBuffersWanted
macro) to determine the number of buffers the renderer requests. Your
application should preload these buffers and send them to the renderer before drawing.
Drawing the Data
You can use the ICDraw
function to decompress the data for drawing. The renderer, however, does not
start drawing data until your application sends the ICM_DRAW_START
message (or uses the ICDrawStart
macro). When your application calls this function, the renderer begins to
draw the frames at the rate specified by the dwRate
parameter divided by the dwScale
parameter; these parameters were supplied when the application initialized
the renderer by using the ICDrawBegin
function. Drawing continues until your application sends the ICM_DRAW_STOP
message (or uses the ICDrawStop
If a renderer buffers the data before drawing, your application should not
use the ICDrawStart
macro until it has sent the number of frames the renderer returned for the ICGetBuffersWanted
parameter of ICDraw
specifies the time to draw a frame. The renderer divides this integer by the
time scale specified with ICDrawBegin
to obtain the actual time. Times for ICDraw
functions are relative to ICDrawStart
sets the clock to zero. For example, if your application specifies 1000 for
the time scale and 75 for lTime
, the renderer draws the frame 75 milliseconds into the sequence.
Controlling Drawing Parameters
You can monitor the clock of a renderer by sending the ICM_DRAW_GETTIME
message (or use the ICDrawGetTime
macro), and you can set the clock of a renderer that can draw data by sending
message (or use the ICDrawSetTime
To change the current position while a renderer is drawing, your application
can send the ICM_DRAW_WINDOW
message (or use the ICDrawWindow
macro) for repositioning the window. Applications typically use this message
whenever the window changes.
If the playback window gets a realize-palette message, your application must
send the ICM_DRAW_REALIZE
message (or use the ICDrawRealize
macro) to have the renderer realize the palette again for playback.
Applications can change the palette by sending the ICM_DRAW_CHANGEPALETTE
message (or use the ICDrawChangePalette
macro) and obtain the current palette by sending the ICM_DRAW_GET_PALETTE
Some renderers must be specifically instructed to display frames passed to
them. Sending the ICM_DRAW_RENDERBUFFER
message (or use the ICDrawRenderBuffer
macro) causes these renderers to draw the frame.
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