Attachment 6425 Details for Bug 7497 – proposed patch

[patch] proposed patch

cairo-color-one-minus-epsilon.patch (text/plain), 4.24 KB, created by Behdad Esfahbod on 2006-08-01 19:20:53 UTC

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Creator: Behdad Esfahbod

Created: 2006-08-01 19:20:53 UTC

Size: 4.24 KB

patch

obsolete

>diff --git a/configure.in b/configure.in
>index 33fc8dc..8ba562d 100644
>--- a/configure.in
>+++ b/configure.in
>@@ -446,11 +446,6 @@ fi
> 
> dnl ===========================================================================
> 
>-AC_CHECK_HEADERS([pthread.h], have_pthread=yes, have_pthread=no)
>-AM_CONDITIONAL(HAVE_PTHREAD, test "x$have_pthread" = "xyes")
>-
>-dnl ===========================================================================
>-
> CAIRO_BACKEND_ENABLE(ps, PostScript, ps, PS_SURFACE, auto, [], [
>   if test x"$have_ft_load_sfnt_table" != "xyes" ; then
>     use_ps="no (requires FreeType 2.1.4 or newer)"
>@@ -527,10 +522,19 @@ CAIRO_BACKEND_ENABLE(atsui, ATSUI font, 
> ])
> 
> dnl ===========================================================================
>+
> dnl Checks for precise integer types
> AC_CHECK_HEADERS([stdint.h inttypes.h sys/int_types.h])
> AC_CHECK_TYPES([uint64_t, uint128_t])
> 
>+dnl Check for misc headers
>+
>+AC_CHECK_HEADERS([float.h])
>+
>+AC_CHECK_HEADERS([pthread.h], have_pthread=yes, have_pthread=no)
>+AM_CONDITIONAL(HAVE_PTHREAD, test "x$have_pthread" = "xyes")
>+
>+
> dnl Use lots of warning flags with GCC
> 
> WARN_CFLAGS=""
>diff --git a/src/cairo-color.c b/src/cairo-color.c
>index e202af2..f612905 100644
>--- a/src/cairo-color.c
>+++ b/src/cairo-color.c
>@@ -89,19 +89,18 @@ _cairo_color_init_rgb (cairo_color_t *co
>     _cairo_color_init_rgba (color, red, green, blue, 1.0);
> }
> 
>-/* We multiply colors by (0x10000 - epsilon), such that we get a uniform
>- * range even for 0xffff.  In other words, (1.0 - epsilon) would convert
>- * to 0xffff, not 0xfffe.
>- */
>-#define CAIRO_COLOR_ONE_MINUS_EPSILON (65536.0 - 1e-5)
>-
> static void
> _cairo_color_compute_shorts (cairo_color_t *color)
> {
>-    color->red_short   = color->red   * color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
>-    color->green_short = color->green * color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
>-    color->blue_short  = color->blue  * color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
>-    color->alpha_short = color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
>+    /* We multiply colors by (65536.0 * (1.0 - epsilon)), such that we get a
>+     * uniform range even for 0xffff.  In other words, (1.0 - epsilon) would
>+     * convert to 0xffff, not 0xfffe when rounded down.  (FIXME: we assume the
>+     * FPU is set to round down.)
>+     */
>+    color->red_short   = color->red   * color->alpha * (65536.0 * CAIRO_ONE_MINUS_EPSILON);
>+    color->green_short = color->green * color->alpha * (65536.0 * CAIRO_ONE_MINUS_EPSILON);
>+    color->blue_short  = color->blue  * color->alpha * (65536.0 * CAIRO_ONE_MINUS_EPSILON);
>+    color->alpha_short = color->alpha *                (65536.0 * CAIRO_ONE_MINUS_EPSILON);
> }
> 
> void
>diff --git a/src/cairoint.h b/src/cairoint.h
>index 4eb0c3c..ee008e9 100644
>--- a/src/cairoint.h
>+++ b/src/cairoint.h
>@@ -168,6 +168,53 @@ # define CAIRO_MUTEX_LOCK(name)
> # define CAIRO_MUTEX_UNLOCK(name)
> #endif
> 
>+#if HAVE_FLOAT_H
>+# include <float.h>
>+#endif
>+#ifndef DBL_EPSILON
>+/* 1e-7 is a conservative value.  it's less than 2^(1-24) which is
>+ * the epsilon value for a 32-bit float.  The regular value for this
>+ * with 64-bit doubles is 2^(1-53) or approximately 1e-16.
>+ */
>+# define DBL_EPSILON 1e-7
>+#endif
>+
>+/* CAIRO_ONE_MINUS_EPSILON:
>+ *
>+ * DBL_EPSILON is the difference between 1 and the least value greater
>+ * than 1 that is representable in the given floating-point type.  Then
>+ * 1.0+DBL_EPSILON looks like:
>+ *
>+ *         1.00000000000...0000000001 * 2**0
>+ *
>+ * while 1.0-DBL_EPSILON looks like:
>+ *
>+ *         0.11111111111...1111111111 * 2**0
>+ *
>+ * and so represented as:
>+ *
>+ *         1.1111111111...11111111110 * 2**-1
>+ *
>+ * so, in fact, 1.0-(DBL_EPSILON*.5) works too, but I don't think it
>+ * really matters.  So, I'll go with the simple 1.0-DBL_EPSILON here.
>+ *
>+ * The following python session shows these observations:
>+ *
>+ *         >>> 1.0 + 2**(1-53)
>+ *         1.0000000000000002
>+ *         >>> 1.0 + 2**(1-54)
>+ *         1.0
>+ *         >>> 1.0 - 2**(1-53)
>+ *         0.99999999999999978
>+ *         >>> 1.0 - 2**(1-54)
>+ *         0.99999999999999989
>+ *         >>> 1.0 - 2**(1-53)*.5
>+ *         0.99999999999999989
>+ *         >>> 1.0 - 2**(1-55)
>+ *         1.0
>+ */
>+#define CAIRO_ONE_MINUS_EPSILON (1.0 - DBL_EPSILON)
>+
> #undef MIN
> #define MIN(a, b) ((a) < (b) ? (a) : (b))
>

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