Conditionally handle linear sRGB in stroke_to func

API-breaking change! This is a temporary measure until the brush dynamics are made color agnostic. Required to get correct HSV/HSL transformations when the brush color is stored as linear sRGB.
odysseywestra · Apr 18, 2020 · 3463f67 · 3463f67
1 parent 5b358df
commit 3463f67
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Showing 4 changed files with 38 additions and 11 deletions.
diff --git a/examples/minimal.c b/examples/minimal.c
@@ -6,8 +6,9 @@ stroke_to(MyPaintBrush *brush, MyPaintSurface *surf, float x, float y)
 {
     float viewzoom = 1.0, viewrotation = 0.0, barrel_rotation = 0.0;
     float pressure = 1.0, ytilt = 0.0, xtilt = 0.0, dtime = 1.0/10;
+    gboolean linear = FALSE
     mypaint_brush_stroke_to
-      (brush, surf, x, y, pressure, xtilt, ytilt, dtime, viewzoom, viewrotation, barrel_rotation);
+      (brush, surf, x, y, pressure, xtilt, ytilt, dtime, viewzoom, viewrotation, barrel_rotation, linear);
 }
 
 int

diff --git a/mypaint-brush.c b/mypaint-brush.c
@@ -1039,7 +1039,7 @@ void print_inputs(MyPaintBrush *self, float* inputs)
   //
   // This is only gets called right after update_states_and_setting_values().
   // Returns TRUE if the surface was modified.
-  gboolean prepare_and_draw_dab (MyPaintBrush *self, MyPaintSurface * surface)
+gboolean prepare_and_draw_dab (MyPaintBrush *self, MyPaintSurface * surface, gboolean linear)
   {
     const float opaque_fac = SETTING(self, OPAQUE_MULTIPLY);
     // ensure we don't get a positive result with two negative opaque values
@@ -1145,8 +1145,25 @@ void print_inputs(MyPaintBrush *self, float* inputs)
       eraser_target_alpha *= (1.0-SETTING(self, ERASER));
     }
 
+    /*
+      If the colors are stored as linear sRGB, they need to be transformed to
+      the form compatible with the hsv/hsl conversion functions, and then
+      transformed back after the adjustments.
+    */
+    gboolean using_hsv_dynamics =
+        SETTING(self, CHANGE_COLOR_H) || SETTING(self, CHANGE_COLOR_HSV_S) || SETTING(self, CHANGE_COLOR_V);
+    gboolean using_hsl_dynamics = SETTING(self, CHANGE_COLOR_L) || SETTING(self, CHANGE_COLOR_HSL_S);
+    gboolean using_color_dynamics = using_hsv_dynamics || using_hsl_dynamics;
+
+    // delinearize
+    if (linear && using_color_dynamics) {
+      color_h = powf(color_h, 1 / 2.2);
+      color_s = powf(color_s, 1 / 2.2);
+      color_v = powf(color_v, 1 / 2.2);
+    }
+
     // HSV color change
-    if (SETTING(self, CHANGE_COLOR_H) || SETTING(self, CHANGE_COLOR_HSV_S) || SETTING(self, CHANGE_COLOR_V)) {
+    if (using_hsv_dynamics) {
         rgb_to_hsv_float(&color_h, &color_s, &color_v);
         color_h += SETTING(self, CHANGE_COLOR_H);
         color_s += color_s * color_v * SETTING(self, CHANGE_COLOR_HSV_S);
@@ -1155,17 +1172,23 @@ void print_inputs(MyPaintBrush *self, float* inputs)
     }
 
     // HSL color change
-    if (SETTING(self, CHANGE_COLOR_L) || SETTING(self, CHANGE_COLOR_HSL_S)) {
+    if (using_hsl_dynamics) {
       // (calculating way too much here, can be optimized if necessary)
       // this function will CLAMP the inputs
-
       rgb_to_hsl_float (&color_h, &color_s, &color_v);
       color_v += SETTING(self, CHANGE_COLOR_L);
       color_s += color_s * MIN(fabsf(1.0f - color_v), fabsf(color_v)) * 2.0f
         * SETTING(self, CHANGE_COLOR_HSL_S);
       hsl_to_rgb_float (&color_h, &color_s, &color_v);
     }
 
+    // linearize
+    if (linear && using_color_dynamics) {
+      color_h = powf(color_h, 2.2);
+      color_s = powf(color_s, 2.2);
+      color_v = powf(color_v, 2.2);
+    }
+
     float hardness = CLAMP(SETTING(self, HARDNESS), 0.0f, 1.0f);
     float softness = CLAMP(SETTING(self, SOFTNESS), 0.0f, 1.0f);
 
@@ -1276,7 +1299,7 @@ void print_inputs(MyPaintBrush *self, float* inputs)
    */
   int mypaint_brush_stroke_to (MyPaintBrush *self, MyPaintSurface *surface,
                                 float x, float y, float pressure,
-                                float xtilt, float ytilt, double dtime, float viewzoom, float viewrotation, float barrel_rotation)
+                               float xtilt, float ytilt, double dtime, float viewzoom, float viewrotation, float barrel_rotation, gboolean linear)
   {
     const float max_dtime = 5;
 
@@ -1323,7 +1346,7 @@ void print_inputs(MyPaintBrush *self, float* inputs)
     if (dtime > 0.100 && pressure && STATE(self, PRESSURE) == 0) {
       // Workaround for tablets that don't report motion events without pressure.
       // This is to avoid linear interpolation of the pressure between two events.
-      mypaint_brush_stroke_to (self, surface, x, y, 0.0, 90.0, 0.0, dtime-0.0001, viewzoom, viewrotation, 0.0);
+      mypaint_brush_stroke_to (self, surface, x, y, 0.0, 90.0, 0.0, dtime-0.0001, viewzoom, viewrotation, 0.0, linear);
       dtime = 0.0001;
     }
 
@@ -1436,7 +1459,7 @@ void print_inputs(MyPaintBrush *self, float* inputs)
 
       // Flips between 1 and -1, used for "mirrored" offsets.
       STATE(self, FLIP) *= -1;
-      gboolean painted_now = prepare_and_draw_dab (self, surface);
+      gboolean painted_now = prepare_and_draw_dab (self, surface, linear);
       if (painted_now) {
         painted = YES;
       } else if (painted == UNKNOWN) {

diff --git a/mypaint-brush.h b/mypaint-brush.h
@@ -45,7 +45,8 @@ mypaint_brush_new_stroke(MyPaintBrush *self);
 
 int
 mypaint_brush_stroke_to(MyPaintBrush *self, MyPaintSurface *surface, float x, float y,
-                        float pressure, float xtilt, float ytilt, double dtime, float viewzoom, float viewrotation, float barrel_rotation);
+                        float pressure, float xtilt, float ytilt, double dtime, float viewzoom,
+                        float viewrotation, float barrel_rotation, gboolean linear);
 
 void
 mypaint_brush_set_base_value(MyPaintBrush *self, MyPaintBrushSetting id, float value);

diff --git a/tests/mypaint-utils-stroke-player.c b/tests/mypaint-utils-stroke-player.c
@@ -139,7 +139,7 @@ mypaint_utils_stroke_player_iterate(MyPaintUtilsStrokePlayer *self)
         last_event_time = last_event->time;
     }
     const float dtime = event->time - last_event_time;
-
+    const float linear = FALSE;
     if (event->valid) {
         if (self->transaction_on_stroke) {
             mypaint_surface_begin_atomic(self->surface);
@@ -148,7 +148,9 @@ mypaint_utils_stroke_player_iterate(MyPaintUtilsStrokePlayer *self)
         mypaint_brush_stroke_to(self->brush, self->surface,
                                 event->x*self->scale, event->y*self->scale,
                                 event->pressure,
-                                event->xtilt, event->ytilt, dtime, event->viewzoom, event->viewrotation, event->barrel_rotation);
+                                event->xtilt, event->ytilt, dtime,
+                                event->viewzoom, event->viewrotation,
+                                event->barrel_rotation, linear);
 
         if (self->transaction_on_stroke) {
             mypaint_surface_end_atomic(self->surface, NULL);