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Emulate proper drawing-tablet behavior via uinput #5

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97 changes: 88 additions & 9 deletions abs-c.c
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Original file line number Diff line number Diff line change
Expand Up @@ -126,15 +126,20 @@ static int handler(void* user, const char* section, const char* name, const char
return 1;
}

int init_uinput(int tmin_x, int tmax_x, int tmin_y, int tmax_y) {
int init_uinput(int tmin_x, int tmax_x, int tmin_y, int tmax_y, int pmin, int pmax) {
int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
if (fd < 0) { perror("open /dev/uinput"); exit(EXIT_FAILURE); }

ioctl(fd, UI_SET_EVBIT, EV_KEY);
ioctl(fd, UI_SET_KEYBIT, BTN_LEFT);
ioctl(fd, UI_SET_KEYBIT, BTN_TOUCH);
ioctl(fd, UI_SET_KEYBIT, BTN_TOOL_PEN);
ioctl(fd, UI_SET_KEYBIT, BTN_STYLUS);
ioctl(fd, UI_SET_EVBIT, EV_ABS);
ioctl(fd, UI_SET_ABSBIT, ABS_X);
ioctl(fd, UI_SET_ABSBIT, ABS_Y);
ioctl(fd, UI_SET_ABSBIT, ABS_PRESSURE);
ioctl(fd, UI_SET_PROPBIT, INPUT_PROP_DIRECT);
ioctl(fd, UI_SET_EVBIT, EV_SYN);

struct uinput_user_dev uidev = {0};
Expand All @@ -147,6 +152,8 @@ int init_uinput(int tmin_x, int tmax_x, int tmin_y, int tmax_y) {
uidev.absmax[ABS_X] = tmax_x;
uidev.absmin[ABS_Y] = tmin_y;
uidev.absmax[ABS_Y] = tmax_y;
uidev.absmin[ABS_PRESSURE] = pmin;
uidev.absmax[ABS_PRESSURE] = pmax;

write(fd, &uidev, sizeof(uidev));
ioctl(fd, UI_DEV_CREATE);
Expand Down Expand Up @@ -213,8 +220,9 @@ void list_devices() {
free(namelist);
}

static inline void emit_abs_delta(int x, int y, bool x_dirty, bool y_dirty) {
struct input_event ev[3];
static inline void emit_tablet_delta(int x, int y, int pressure,
bool x_dirty, bool y_dirty, bool p_dirty) {
struct input_event ev[4];
int n = 0;

if (x_dirty) {
Expand All @@ -233,6 +241,14 @@ static inline void emit_abs_delta(int x, int y, bool x_dirty, bool y_dirty) {
};
}

if (p_dirty) {
ev[n++] = (struct input_event){
.type = EV_ABS,
.code = ABS_PRESSURE,
.value = pressure
};
}

// Always terminate with SYN
ev[n++] = (struct input_event){
.type = EV_SYN,
Expand Down Expand Up @@ -335,6 +351,14 @@ int main(int argc, char *argv[]) {
ioctl(fd, EVIOCGABS(ABS_Y), &absinfo);
int tmin_y = absinfo.minimum, tmax_y = absinfo.maximum;

int pmin = 0, pmax = 1023;
bool has_pressure = false;
if (ioctl(fd, EVIOCGABS(ABS_PRESSURE), &absinfo) == 0) {
pmin = absinfo.minimum;
pmax = absinfo.maximum;
has_pressure = true;
}

double sr = (double)config.display_width / config.display_height;
float x_center = (tmin_x + tmax_x)/2.0f + config.x_offset_pct*0.01f*(tmax_x-tmin_x)/2.0f;
float y_center = (tmin_y + tmax_y)/2.0f + config.y_offset_pct*0.01f*(tmax_y-tmin_y)/2.0f;
Expand All @@ -356,16 +380,19 @@ int main(int argc, char *argv[]) {
int new_tmin_y = (int)(y_center - y_half_range);
int new_tmax_y = (int)(y_center + y_half_range);

tab_fd = init_uinput(new_tmin_x, new_tmax_x, new_tmin_y, new_tmax_y);
tab_fd = init_uinput(new_tmin_x, new_tmax_x, new_tmin_y, new_tmax_y, pmin, pmax);

struct sched_param param = {.sched_priority=20};
sched_setscheduler(0, SCHED_FIFO, &param);
mlockall(MCL_CURRENT | MCL_FUTURE);

struct pollfd pfd = {.fd=fd, .events=POLLIN};

int x = 0, y = 0;
int x_old = -1, y_old = -1;
int x = 0, y = 0, pressure = pmin;
int x_old = -1, y_old = -1, pressure_old = -1;
int pressure_hover = pmin > 0 ? pmin : 1;
bool pen_in_range = false;
bool touching = false;
bool active = false;
bool grabbed = false;

Expand All @@ -382,6 +409,7 @@ int main(int argc, char *argv[]) {
clock_gettime(CLOCK_MONOTONIC, &ts_last);

printf("Press Ctrl-C to quit\n");
bool was_active = active;
while (!stop) {
struct timespec ts_now;
clock_gettime(CLOCK_MONOTONIC, &ts_now);
Expand All @@ -395,6 +423,22 @@ int main(int argc, char *argv[]) {
// Update device grab based on state
set_grab(fd, &grabbed, active);

if (was_active && !active) {
struct input_event out_of_range[4] = {
{ .type = EV_KEY, .code = BTN_LEFT, .value = 0 },
{ .type = EV_KEY, .code = BTN_TOUCH, .value = 0 },
{ .type = EV_KEY, .code = BTN_TOOL_PEN, .value = 0 },
{ .type = EV_SYN, .code = SYN_REPORT, .value = 0 }
};
write(tab_fd, out_of_range, sizeof(out_of_range));
pressure = pmin;
emit_tablet_delta(x, y, pressure, false, false, true);
pressure_old = pressure;
touching = false;
pen_in_range = false;
}
was_active = active;

if (active == true) {
int poll_rc = poll(&pfd, 1, -1);
if (poll_rc == -1) {
Expand All @@ -421,6 +465,7 @@ int main(int argc, char *argv[]) {

bool x_dirty = false;
bool y_dirty = false;
bool p_dirty = false;

if (ev.type == EV_ABS) {
if (ev.code == ABS_X && ev.value != x_old) {
Expand All @@ -431,23 +476,57 @@ int main(int argc, char *argv[]) {
y = ev.value;
y_dirty = true;
}
else if (ev.code == ABS_PRESSURE && has_pressure && ev.value != pressure_old) {
pressure = ev.value;
p_dirty = true;
}

if ((x_dirty || y_dirty || p_dirty) && !pen_in_range) {
struct input_event pen_ev[2] = {
{ .type = EV_KEY, .code = BTN_TOOL_PEN, .value = 1 },
{ .type = EV_SYN, .code = SYN_REPORT, .value = 0 }
};
write(tab_fd, pen_ev, sizeof(pen_ev));
pen_in_range = true;
}

if (x_dirty || y_dirty) {
emit_abs_delta(x, y, x_dirty, y_dirty);
if (x_dirty || y_dirty || p_dirty) {
emit_tablet_delta(x, y, pressure, x_dirty, y_dirty, p_dirty);
x_old = x;
y_old = y;
pressure_old = pressure;
}
}

if (config.enable_buttons &&
ev.type == EV_KEY &&
ev.code == BTN_LEFT) {
Comment on lines 501 to 503
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@chatgpt-codex-connector chatgpt-codex-connector Bot Apr 15, 2026

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P2 Badge Emit BTN_TOUCH for pressure-only input paths

Contact reporting is currently gated on EV_KEY/BTN_LEFT, so devices that provide ABS_PRESSURE but do not emit BTN_LEFT never produce BTN_TOUCH transitions. Since this commit now advertises tablet keys and forwards pressure, pressure-capable sources can still fail to register pen-down in apps that require BTN_TOUCH (common in tablet input handling).

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touching = ev.value != 0;
if (!has_pressure) {
pressure = touching ? pressure_hover : pmin;
if (pressure != pressure_old) {
emit_tablet_delta(x, y, pressure, false, false, true);
pressure_old = pressure;
}
}

if (touching && !pen_in_range) {
struct input_event in_range[2] = {
{ .type = EV_KEY, .code = BTN_TOOL_PEN, .value = 1 },
{ .type = EV_SYN, .code = SYN_REPORT, .value = 0 }
};
write(tab_fd, in_range, sizeof(in_range));
pen_in_range = true;
}

struct input_event btn[2] = {
struct input_event btn[4] = {
{ .type = EV_KEY, .code = BTN_LEFT, .value = ev.value },
{ .type = EV_KEY, .code = BTN_TOUCH, .value = ev.value },
{ .type = EV_KEY, .code = BTN_TOOL_PEN, .value = touching ? 1 : 0 },
{ .type = EV_SYN, .code = SYN_REPORT, .value = 0 }
};
write(tab_fd, btn, sizeof(btn));
pen_in_range = touching;
Comment on lines +525 to +529
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@chatgpt-codex-connector chatgpt-codex-connector Bot Apr 15, 2026

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P2 Badge Keep BTN_TOOL_PEN asserted while pointer remains in range

On every BTN_LEFT release this block emits BTN_TOOL_PEN=0 and immediately sets pen_in_range=false, even if the finger/stylus is still producing ABS movement. That creates spurious out-of-range/in-range transitions around normal click-release actions (the next ABS event re-asserts range), which can reset hover state or fragment strokes in tablet consumers.

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}
}
else {
Expand Down