On Tue, Oct 9, 2012 at 2:14 AM, Olivier Fourdan <ofour...@redhat.com> wrote:
> Hi all,
>
> I've been wondering, the BuiltIn flag (discussed earlier) is also set
> automatically on Linux in get_device_info() in libwacom/libwacom.c:
>
> 113 static gboolean
> 114 get_device_info (const char *path,
> ...
> 121 {
> ...
> 157 /* Is the device builtin? */
> 158 devname = g_udev_device_get_name (device);
> 159 if (devname != NULL) {
> 160 char *sysfs_path, *contents;
> 161
> 162 sysfs_path = g_build_filename
> ("/sys/class/input", devname, "device/properties", NULL);
> 163 if (g_file_get_contents (sysfs_path, &contents,
> NULL, NULL)) {
> 164 int flag;
> 165
> 166 /* 0x01: POINTER flag
> 167 * 0x02: DIRECT flag */
> 168 flag = atoi(contents);
> 169 *builtin = (flag & 0x02) == 0x02 ?
> IS_BUILTIN_TRUE : IS_BUILTIN_FALSE;
> 170 g_free (contents);
> 171 }
> 172 g_free (sysfs_path);
> 173 }
>
> So I have been wondering about that flag 0x02used here.
>
> /usr/include/linux/input.h has the following:
>
> 155 /*
> 156 * Device properties and quirks
> 157 */
> 158
> 159 #define INPUT_PROP_POINTER 0x00 /* needs a
> pointer */
> 160 #define INPUT_PROP_DIRECT 0x01 /* direct input
> devices */
> 161 #define INPUT_PROP_BUTTONPAD 0x02 /* has
> button(s) under pad */
> 162 #define INPUT_PROP_SEMI_MT 0x03 /* touch
> rectangle only */
> 163
> 164 #define INPUT_PROP_MAX 0x1f
> 165 #define INPUT_PROP_CNT (INPUT_PROP_MAX + 1)
> 166
>
> But there INPUT_PROP_DIRECT is 0x01 not 0x02 (0x02 is BUTTONPAD).
>
> Is really 0x02 what we want here? And if I am misunderstanding, why
> not using definitions names rather than cryptic bit flags directly?
>
> Cheers,
> Olivier
>
INPUT_PROP_* aren't bit flags -- they're bit positions. That is, if
bit number INPUT_PROP_DIRECT is set, then it's a direct input device.
Or, put differently (and grabbing descriptions from event-codes.txt):
if (flag & (1 << INPUT_PROP_POINTER)) {
// The INPUT_PROP_POINTER property indicates that the device is not transposed
// on the screen and thus requires use of an on-screen pointer to trace user's
// movements. Typical pointer devices: touchpads, tablets, mice; non-pointer
// device: touchscreen.
}
if (flag & (1 << INPUT_PROP_DIRECT)) {
// The INPUT_PROP_DIRECT property indicates that device coordinates should be
// directly mapped to screen coordinates (not taking into account trivial
// transformations, such as scaling, flipping and rotating). Non-direct input
// devices require non-trivial transformation, such as absolute to relative
// transformation for touchpads. Typical direct input devices: touchscreens,
// drawing tablets; non-direct devices: touchpads, mice.
}
Note that INPUT_PROP_DIRECT is specified to be set for both
touchscreens (e.g. Cintiq, tablet PC) *and* for drawing tablets (e.g.
Intuos, Bamboo). To properly ensure that you're getting a touchscreen,
you need to make sure that its DIRECT and non-POINTER. Because of
this, the libwacom code technically isn't correct; the only reason it
doesn't think an Intuos is built-in is because the guidelines weren't
clear when my kernel patches were accepted and so they don't have the
DIRECT flag set.
To be correct and use the defines instead of hex codes, it should
probably be written more like:
int hw_flags = atoi(contents);
int direct_flag = (1 << INPUT_PROP_DIRECT);
int pointer_flag = (1 << INPUT_PROP_POINTER);
*builtin = (hw_flags & (direct_flag | pointer_flag) == direct_flag) ?
IS_BUILTIN_TRUE : IS_BUILTIN_FALSE;
Jason
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