From 9d6ed04dffcfe65bd98d45df78c4ecc5d1d371ff Mon Sep 17 00:00:00 2001 From: Federico Mena Quintero Date: Wed, 7 Jan 2004 03:16:10 +0000 Subject: [PATCH] Added a section on how to compute pixel offsets for 2004-01-06 Federico Mena Quintero * gdk-pixbuf/tmpl/gdk-pixbuf.sgml: Added a section on how to compute pixel offsets for gdk_pixbuf_get_pixels(). --- docs/reference/ChangeLog | 5 + .../reference/gdk-pixbuf/tmpl/gdk-pixbuf.sgml | 121 ++++++++++++++++++ 2 files changed, 126 insertions(+) diff --git a/docs/reference/ChangeLog b/docs/reference/ChangeLog index f077eda35d..0834d38e83 100644 --- a/docs/reference/ChangeLog +++ b/docs/reference/ChangeLog @@ -15,6 +15,11 @@ Wed Jan 7 01:26:07 2004 Matthias Clasen * gdk-pixbuf/gdk-pixbuf-sections.txt: Add gdk_pixbuf_get_file_info. +2004-01-06 Federico Mena Quintero + + * gdk-pixbuf/tmpl/gdk-pixbuf.sgml: Added a section on how to + compute pixel offsets for gdk_pixbuf_get_pixels(). + Mon Dec 29 01:40:20 2003 Matthias Clasen * gtk/gtk-sections.txt: Add gtk_accel_map_{un,}lock_path. diff --git a/docs/reference/gdk-pixbuf/tmpl/gdk-pixbuf.sgml b/docs/reference/gdk-pixbuf/tmpl/gdk-pixbuf.sgml index 728ae31d1b..7cbef5a28d 100644 --- a/docs/reference/gdk-pixbuf/tmpl/gdk-pixbuf.sgml +++ b/docs/reference/gdk-pixbuf/tmpl/gdk-pixbuf.sgml @@ -11,6 +11,81 @@ Information that describes an image. information that describes an image in memory. +
+ Image Data + + + Image data in a pixbuf is stored in memory in uncompressed, + packed format. Rows in the image are stored top to bottom, and + in each row pixels are stored from left to right. There may be + padding at the end of a row. The "rowstride" value of a pixbuf, + as returned by gdk_pixbuf_get_rowstride(), indicates the number + of bytes between rows. + + + + put_pixel() example + + + The following code illustrates a simple put_pixel() function + for RGB pixbufs with 8 bits per channel with an alpha channel. + It is not included in the gdk-pixbuf library for performance + reasons; rather than making several function calls for each + pixel, your own code can take shortcuts. + + + +static void +put_pixel (GdkPixbuf *pixbuf, int x, int y, guchar red, guchar green, guchar blue, guchar alpha) +{ + int width, height, rowstride, n_channels; + guchar *pixels, *p; + + n_channels = gdk_pixbuf_get_n_channels (pixbuf); + + g_assert (gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB); + g_assert (gdk_pixbuf_get_bits_per_sample (pixbuf) == 8); + g_assert (gdk_pixbuf_get_has_alpha (pixbuf)); + g_assert (n_channels == 4); + + width = gdk_pixbuf_get_width (pixbuf); + height = gdk_pixbuf_get_height (pixbuf); + + g_assert (x >= 0 && x < width); + g_assert (y >= 0 && y < height); + + rowstride = gdk_pixbuf_get_rowstride (pixbuf); + pixels = gdk_pixbuf_get_pixels (pixbuf); + + p = pixels + y * rowstride + x * n_channels; + p[0] = red; + p[1] = green; + p[2] = blue; + p[3] = alpha; +} + + + + This function will not work for pixbufs with images that are + other than 8 bits per sample or channel, but it will work for + most of the pixbufs that GTK+ uses. + + + + + + If you are doing memcpy() of raw pixbuf data, note that the + last row in the pixbuf may not be as wide as the full + rowstride, but rather just as wide as the pixel data needs to + be. That is, it is unsafe to do memcpy (dest, + pixels, rowstride * height) to copy a whole pixbuf. + Use gdk_pixbuf_copy() instead, or compute the width in bytes + of the last row as width * ((n_channels * + bits_per_sample + 7) / 8). + + +
+ @@ -76,6 +151,46 @@ In the future it will do full alpha compositing. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + @@ -163,3 +278,9 @@ End: @Returns: +