pbio/drv/display, pybricks.parameters: Improve conversion from HSV to pixel value.

lib/pbio/drv/display/display_ev3.c

@@ -486,6 +486,34 @@ uint8_t pbdrv_display_get_max_value(void) {
     return ST7586S_VALUE_MAX;
 }
 
+uint8_t pbdrv_display_get_value_from_hsv(uint16_t h, uint8_t s, uint8_t v) {
+    // Method to compute those values: take a picture of the EV3 screen
+    // displaying the four gray levels, take a sample for each level, then,
+    // using python:
+    //
+    // import numpy as np
+    // measures = np.array([28, 36, 41, 47]) # %
+    // measures = measures - measures[0]
+    // measures = measures / measures[-1] * 100 * 100
+    // splits = (measures[0:-1] + measures[1:]) / 2
+    // print([int(x) for x in splits])
+    static const uint16_t splits_x100[] = { 2105, 5526, 8421 };
+    uint16_t l_x100 = v * (100 - s / 2);
+    if (l_x100 < splits_x100[1]) {
+        if (l_x100 < splits_x100[0]) {
+            return 3;
+        } else {
+            return 2;
+        }
+    } else {
+        if (l_x100 < splits_x100[2]) {
+            return 1;
+        } else {
+            return 0;
+        }
+    }
+}
+
 void pbdrv_display_update(void) {
     pbdrv_display_user_frame_update_requested = true;
     pbio_os_request_poll();

lib/pbio/drv/display/display_virtual.c

@@ -87,6 +87,25 @@ uint8_t pbdrv_display_get_max_value(void) {
     return 3;
 }
 
+uint8_t pbdrv_display_get_value_from_hsv(uint16_t h, uint8_t s, uint8_t v) {
+    // Method to compute those values: see EV3 driver.
+    static const uint16_t splits_x100[] = { 2105, 5526, 8421 };
+    uint16_t l_x100 = v * (100 - s / 2);
+    if (l_x100 < splits_x100[1]) {
+        if (l_x100 < splits_x100[0]) {
+            return 3;
+        } else {
+            return 2;
+        }
+    } else {
+        if (l_x100 < splits_x100[2]) {
+            return 1;
+        } else {
+            return 0;
+        }
+    }
+}
+
 void pbdrv_display_update(void) {
     pbdrv_display_user_frame_update_requested = true;
     pbio_os_request_poll();

lib/pbio/include/pbdrv/display.h

@@ -26,6 +26,15 @@ pbio_image_t *pbdrv_display_get_image(void);
  */
 uint8_t pbdrv_display_get_max_value(void);
 
+/**
+ * Get the pixel value corresponding to a color given in HSV space.
+ * @param [in] h  Hue, 0 to 359 degrees.
+ * @param [in] s  Saturation, 0 to 100 percent.
+ * @param [in] v  Value, 0 to 100 percent.
+ * @return  Pixel value.
+ */
+uint8_t pbdrv_display_get_value_from_hsv(uint16_t h, uint8_t s, uint8_t v);
+
 /**
  * Update the display to show current content of image container.
  */
@@ -41,6 +50,10 @@ static inline uint8_t pbdrv_display_get_max_value(void) {
     return 0;
 }
 
+static inline uint8_t pbdrv_display_get_value_from_hsv(uint16_t h, uint8_t s, uint8_t v) {
+    return 0;
+}
+
 static inline void pbdrv_display_update(void) {
 }
 

pybricks/parameters/pb_type_image.c

@@ -44,8 +44,7 @@ static int get_color(mp_obj_t obj) {
         return mp_obj_get_int(obj);
     }
     const pbio_color_hsv_t *hsv = pb_type_Color_get_hsv(obj);
-    int32_t v = pbio_int_math_bind(hsv->v, 0, 100);
-    return max - v * max / 100;
+    return pbdrv_display_get_value_from_hsv(hsv->h, hsv->s, hsv->v);
 }
 
 mp_obj_t pb_type_Image_display_obj_new(void) {