[vlc-devel] [PATCH] png: add encoder

[Tristan Matthews]

This patch adds a basic encoder to the png module (using libpng).

---
 modules/codec/png.c | 181 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 178 insertions(+), 3 deletions(-)

diff --git a/modules/codec/png.c b/modules/codec/png.c
index b4d6ef4..7bb0320 100644
--- a/modules/codec/png.c
+++ b/modules/codec/png.c
@@ -49,6 +49,20 @@ static void CloseDecoder  ( vlc_object_t * );
 
 static picture_t *DecodeBlock  ( decoder_t *, block_t ** );
 
+/*
+ * png encoder descriptor
+ */
+struct encoder_sys_t
+{
+    int i_blocksize;
+    bool b_error;
+};
+
+static int  OpenEncoder(vlc_object_t *);
+static void CloseEncoder(vlc_object_t *);
+
+static block_t *EncodeBlock(encoder_t *, picture_t *);
+
 /*****************************************************************************
  * Module descriptor
  *****************************************************************************/
@@ -59,6 +73,14 @@ vlc_module_begin ()
     set_capability( "decoder", 1000 )
     set_callbacks( OpenDecoder, CloseDecoder )
     add_shortcut( "png" )
+
+    /* encoder submodule */
+    add_submodule()
+    add_shortcut("png")
+    set_section(N_("Encoding"), NULL)
+    set_description(N_("PNG video encoder"))
+    set_capability("encoder", 1000)
+    set_callbacks(OpenEncoder, CloseEncoder)
 vlc_module_end ()
 
 /*****************************************************************************
@@ -101,19 +123,51 @@ static void user_read( png_structp p_png, png_bytep data, png_size_t i_length )
     p_block->i_buffer -= i_length;
 }
 
-static void user_error( png_structp p_png, png_const_charp error_msg )
+static void user_flush( png_structp p_png )
+{
+    /* noop */
+    (void) p_png;
+}
+
+static void user_write( png_structp p_png, png_bytep data, png_size_t i_length )
+{
+    block_t *p_block = (block_t *)png_get_io_ptr( p_png );
+    if( i_length > p_block->i_buffer ) {
+        png_error( p_png, "not enough data" );
+        return;
+    }
+
+    memcpy( p_block->p_buffer, data, i_length );
+    p_block->p_buffer += i_length;
+    p_block->i_buffer -= i_length;
+}
+
+static void user_decoder_error( png_structp p_png, png_const_charp error_msg )
 {
     decoder_t *p_dec = (decoder_t *)png_get_error_ptr( p_png );
     p_dec->p_sys->b_error = true;
     msg_Err( p_dec, "%s", error_msg );
 }
 
-static void user_warning( png_structp p_png, png_const_charp warning_msg )
+static void user_encoder_error( png_structp p_png, png_const_charp error_msg )
+{
+    encoder_t *p_enc = (encoder_t*)png_get_error_ptr( p_png );
+    p_enc->p_sys->b_error = true;
+    msg_Err( p_enc, "%s", error_msg );
+}
+
+static void user_decoder_warning( png_structp p_png, png_const_charp warning_msg )
 {
     decoder_t *p_dec = (decoder_t *)png_get_error_ptr( p_png );
     msg_Warn( p_dec, "%s", warning_msg );
 }
 
+static void user_encoder_warning( png_structp p_png, png_const_charp warning_msg )
+{
+    encoder_t *p_enc = (encoder_t *)png_get_error_ptr( p_png );
+    msg_Warn( p_enc, "%s", warning_msg );
+}
+
 /****************************************************************************
  * DecodeBlock: the whole thing
  ****************************************************************************
@@ -172,7 +226,7 @@ static picture_t *DecodeBlock( decoder_t *p_dec, block_t **pp_block )
         goto error;
 
     png_set_read_fn( p_png, (void *)p_block, user_read );
-    png_set_error_fn( p_png, (void *)p_dec, user_error, user_warning );
+    png_set_error_fn( p_png, (void *)p_dec, user_decoder_error, user_decoder_warning );
 
     png_read_info( p_png, p_info );
     if( p_sys->b_error ) goto error;
@@ -253,3 +307,124 @@ static void CloseDecoder( vlc_object_t *p_this )
 
     free( p_sys );
 }
+
+static int OpenEncoder(vlc_object_t *p_this)
+{
+    encoder_t *p_enc = (encoder_t *) p_this;
+
+    if( p_enc->fmt_out.i_codec != VLC_CODEC_PNG )
+        return VLC_EGENERIC;
+
+    /* Allocate the memory needed to store the encoder's structure */
+    if( ( p_enc->p_sys = malloc(sizeof(encoder_sys_t)) ) == NULL )
+        return VLC_ENOMEM;
+
+    p_enc->p_sys->i_blocksize = 3 * p_enc->fmt_in.video.i_visible_width *
+        p_enc->fmt_in.video.i_visible_height;
+
+    p_enc->fmt_in.i_codec = VLC_CODEC_RGB24;
+    p_enc->fmt_in.video.i_rmask = 0x000000ff;
+    p_enc->fmt_in.video.i_gmask = 0x0000ff00;
+    p_enc->fmt_in.video.i_bmask = 0x00ff0000;
+    p_enc->pf_encode_video = EncodeBlock;
+
+    return VLC_SUCCESS;
+}
+
+/*
+ * EncodeBlock
+ */
+static block_t *EncodeBlock(encoder_t *p_enc, picture_t *p_pic)
+{
+    encoder_sys_t *p_sys = p_enc->p_sys;
+
+    if( unlikely( !p_pic ) )
+    {
+        return NULL;
+    }
+
+    block_t *p_block = block_Alloc( p_sys->i_blocksize );
+    if( p_block == NULL )
+    {
+        return NULL;
+    }
+
+    png_structp p_png = png_create_write_struct( PNG_LIBPNG_VER_STRING, 0, 0, 0 );
+    if( p_png == NULL )
+    {
+        block_Release( p_block );
+        return NULL;
+    }
+
+    /* save buffer start */
+    void *start = p_block->p_buffer;
+
+    p_sys->b_error = false;
+
+    /* libpng longjmp's there in case of error */
+    if( setjmp( png_jmpbuf( p_png ) ) )
+        goto error;
+
+    png_set_write_fn( p_png, p_block, user_write, user_flush );
+    png_set_error_fn( p_png, p_enc, user_encoder_error, user_encoder_warning );
+
+    png_infop p_info = png_create_info_struct( p_png );
+    if( p_info == NULL )
+    {
+        png_destroy_write_struct( &p_png, NULL );
+        block_Release( p_block );
+        return NULL;
+    }
+
+    png_infop p_end_info = png_create_info_struct( p_png );
+    if( p_end_info == NULL ) goto error;
+
+    const unsigned i_width = p_enc->fmt_in.video.i_visible_width;
+    const unsigned i_height = p_enc->fmt_in.video.i_visible_height;
+
+    png_set_IHDR( p_png, p_info,
+            i_width,
+            i_height,
+            8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
+            PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT );
+    if( p_sys->b_error ) goto error;
+
+    png_write_info( p_png, p_info );
+    if( p_sys->b_error ) goto error;
+
+    /* Encode picture */
+
+    for( unsigned i = 0; i < i_height; i++ )
+    {
+        png_write_row( p_png, p_pic->p->p_pixels + (i_width * i * 3));
+        if( p_sys->b_error ) goto error;
+    }
+
+    png_write_end( p_png, p_end_info );
+    if( p_sys->b_error ) goto error;
+
+    png_destroy_write_struct( &p_png, &p_info );
+
+    /* restore original buffer position */
+    p_block->p_buffer = start;
+    return p_block;
+
+ error:
+
+    png_destroy_write_struct( &p_png, &p_info );
+
+    p_block->p_buffer = start;
+    block_Release(p_block);
+    return NULL;
+}
+
+/*****************************************************************************
+ * CloseEncoder: png encoder destruction
+ *****************************************************************************/
+static void CloseEncoder( vlc_object_t *p_this )
+{
+    encoder_t *p_enc = (encoder_t *)p_this;
+    encoder_sys_t *p_sys = p_enc->p_sys;
+
+    free( p_sys );
+}
-- 
1.8.3.2