Rework the pixel computation to use areas

This changes the displayio pixel computation from per-pixel to
per-area. This is precursor work to updating portions of the screen
(#1169). It should provide mild speedups because bounds checks are
done once per area rather than once per pixel. Filling by area also
allows TileGrid to maintain a row-associative fill pattern even when
the display's refresh is orthogonal to it.

1 files changed, 114 insertions, 35 deletions

diff --git a/shared-module/displayio/TileGrid.c b/shared-module/displayio/TileGrid.c
index 3212dfe8b..6ffc65889 100644
--- a/shared-module/displayio/TileGrid.c
+++ b/shared-module/displayio/TileGrid.c
@@ -56,31 +56,40 @@ void common_hal_displayio_tilegrid_construct(displayio_tilegrid_t *self, mp_obj_
     self->bitmap_width_in_tiles = bitmap_width_in_tiles;
     self->width_in_tiles = width;
     self->height_in_tiles = height;
-    self->total_width = width * tile_width;
-    self->total_height = height * tile_height;
+    self->area.x1 = x;
+    self->area.y1 = y;
+    // -1 because areas are inclusive
+    self->area.x2 = x + width * tile_width - 1;
+    self->area.y2 = y + height * tile_height - 1;
     self->tile_width = tile_width;
     self->tile_height = tile_height;
     self->bitmap = bitmap;
     self->pixel_shader = pixel_shader;
-    self->x = x;
-    self->y = y;
 }
 
 
 mp_int_t common_hal_displayio_tilegrid_get_x(displayio_tilegrid_t *self) {
-    return self->x;
+    return self->area.x1;
 }
 void common_hal_displayio_tilegrid_set_x(displayio_tilegrid_t *self, mp_int_t x) {
-    self->needs_refresh = self->x != x;
-    self->x = x;
+    if (self->area.x1 == x) {
+        return;
+    }
+    self->needs_refresh = true;
+    self->area.x2 += (self->area.x1 - x);
+    self->area.x1 = x;
 }
 mp_int_t common_hal_displayio_tilegrid_get_y(displayio_tilegrid_t *self) {
-    return self->y;
+    return self->area.y1;
 }
 
 void common_hal_displayio_tilegrid_set_y(displayio_tilegrid_t *self, mp_int_t y) {
-    self->needs_refresh = self->y != y;
-    self->y = y;
+    if (self->area.y1 == y) {
+        return;
+    }
+    self->needs_refresh = true;
+    self->area.y2 += (self->area.y1 - y);
+    self->area.y1 = y;
 }
 
 mp_obj_t common_hal_displayio_tilegrid_get_pixel_shader(displayio_tilegrid_t *self) {
@@ -128,14 +137,11 @@ void common_hal_displayio_tilegrid_set_tile(displayio_tilegrid_t *self, uint16_t
 void common_hal_displayio_tilegrid_set_top_left(displayio_tilegrid_t *self, uint16_t x, uint16_t y) {
     self->top_left_x = x;
     self->top_left_y = y;
+    self->needs_refresh = true;
 }
-bool displayio_tilegrid_get_pixel(displayio_tilegrid_t *self, int16_t x, int16_t y, uint16_t* pixel) {
-    x -= self->x;
-    y -= self->y;
-    if (y < 0 || y >= self->total_height || x >= self->total_width || x < 0) {
-        return false;
-    }
 
+bool displayio_tilegrid_get_area(displayio_tilegrid_t *self, displayio_buffer_transform_t* transform, displayio_area_t* area, uint32_t* mask, uint32_t *buffer) {
+    // If no tiles are present we have no impact.
     uint8_t* tiles = self->tiles;
     if (self->inline_tiles) {
         tiles = (uint8_t*) &self->tiles;
@@ -143,30 +149,103 @@ bool displayio_tilegrid_get_pixel(displayio_tilegrid_t *self, int16_t x, int16_t
     if (tiles == NULL) {
         return false;
     }
-    uint16_t tile_location = ((y / self->tile_height + self->top_left_y) % self->height_in_tiles) * self->width_in_tiles + (x / self->tile_width + self->top_left_x) % self->width_in_tiles;
-    uint8_t tile = tiles[tile_location];
-    uint16_t tile_x = tile_x = (tile % self->bitmap_width_in_tiles) * self->tile_width + x % self->tile_width;
-    uint16_t tile_y = tile_y = (tile / self->bitmap_width_in_tiles) * self->tile_height + y % self->tile_height;
 
-    uint32_t value = 0;
-    if (MP_OBJ_IS_TYPE(self->bitmap, &displayio_bitmap_type)) {
-        value = common_hal_displayio_bitmap_get_pixel(self->bitmap, tile_x, tile_y);
-    } else if (MP_OBJ_IS_TYPE(self->bitmap, &displayio_shape_type)) {
-        value = common_hal_displayio_shape_get_pixel(self->bitmap, tile_x, tile_y);
-    } else if (MP_OBJ_IS_TYPE(self->bitmap, &displayio_ondiskbitmap_type)) {
-        value = common_hal_displayio_ondiskbitmap_get_pixel(self->bitmap, tile_x, tile_y);
+    displayio_area_t overlap;
+    displayio_area_t scaled_area = {
+        .x1 = self->area.x1 * transform->scale,
+        .y1 = self->area.y1 * transform->scale,
+        .x2 = (self->area.x2 + 1) * transform->scale - 1, // Second point is inclusive.
+        .y2 = (self->area.y2 + 1) * transform->scale - 1
+    };
+    if (!displayio_area_compute_overlap(area, &scaled_area, &overlap)) {
+        return false;
     }
 
-    if (self->pixel_shader == mp_const_none) {
-        *pixel = value;
-        return true;
-    } else if (MP_OBJ_IS_TYPE(self->pixel_shader, &displayio_palette_type) && displayio_palette_get_color(self->pixel_shader, value, pixel)) {
-        return true;
-    } else if (MP_OBJ_IS_TYPE(self->pixel_shader, &displayio_colorconverter_type) && common_hal_displayio_colorconverter_convert(self->pixel_shader, value, pixel)) {
-        return true;
+    int16_t x_stride = 1;
+    int16_t y_stride = displayio_area_width(area);
+    if (transform->transpose_xy) {
+        x_stride = displayio_area_height(area);
+        y_stride = 1;
+    }
+    uint16_t start = 0;
+    if (transform->mirror_x) {
+        start += (area->x2 - area->x1) * x_stride;
+        x_stride *= -1;
+    }
+    if (transform->mirror_y) {
+        start += (area->y2 - area->y1) * y_stride;
+        y_stride *= -1;
     }
 
-    return false;
+    bool full_coverage = displayio_area_equal(area, &overlap);
+
+    // TODO(tannewt): Set full coverage to true if all pixels outside the overlap have already been
+    // set as well.
+    bool always_full_coverage = false;
+
+    // TODO(tannewt): Check to see if the pixel_shader has any transparency. If it doesn't then we
+    // can either return full coverage or bulk update the mask.
+    int16_t y = overlap.y1 - scaled_area.y1;
+    if (y < 0) {
+        y = 0;
+    }
+    int16_t x_shift = area->x1 - scaled_area.x1;
+    int16_t y_shift = area->y1 - scaled_area.y1;
+    for (; y <= overlap.y2 - scaled_area.y1; y++) {
+        int16_t x = overlap.x1 - scaled_area.x1;
+        if (x < 0) {
+            x = 0;
+        }
+        int16_t row_start = start + (y - y_shift) * y_stride;
+        int16_t local_y = y / transform->scale;
+        for (; x <= overlap.x2 - scaled_area.x1; x++) {
+            // Compute the destination pixel in the buffer and mask based on the transformations.
+            uint16_t offset = row_start + (x - x_shift) * x_stride;
+
+            // Check the mask first to see if the pixel has already been set.
+            if ((mask[offset / 32] & (1 << (offset % 32))) != 0) {
+                continue;
+            }
+            int16_t local_x = x / transform->scale;
+            uint16_t tile_location = ((local_y / self->tile_height + self->top_left_y) % self->height_in_tiles) * self->width_in_tiles + (local_x / self->tile_width + self->top_left_x) % self->width_in_tiles;
+            uint8_t tile = tiles[tile_location];
+            uint16_t tile_x = (tile % self->bitmap_width_in_tiles) * self->tile_width + local_x % self->tile_width;
+            uint16_t tile_y = (tile / self->bitmap_width_in_tiles) * self->tile_height + local_y % self->tile_height;
+
+            uint32_t value = 0;
+            // We always want to read bitmap pixels by row first and then transpose into the destination
+            // buffer because most bitmaps are row associated.
+            if (MP_OBJ_IS_TYPE(self->bitmap, &displayio_bitmap_type)) {
+                value = common_hal_displayio_bitmap_get_pixel(self->bitmap, tile_x, tile_y);
+            } else if (MP_OBJ_IS_TYPE(self->bitmap, &displayio_shape_type)) {
+                value = common_hal_displayio_shape_get_pixel(self->bitmap, tile_x, tile_y);
+            } else if (MP_OBJ_IS_TYPE(self->bitmap, &displayio_ondiskbitmap_type)) {
+                value = common_hal_displayio_ondiskbitmap_get_pixel(self->bitmap, tile_x, tile_y);
+            }
+
+            uint16_t* pixel = ((uint16_t*) buffer) + offset;
+            if (self->pixel_shader == mp_const_none) {
+                *pixel = value;
+                return true;
+            } else if (MP_OBJ_IS_TYPE(self->pixel_shader, &displayio_palette_type)) {
+                if (!displayio_palette_get_color(self->pixel_shader, value, pixel)) {
+                    // mark the pixel as transparent
+                    full_coverage = false;
+                } else if (!always_full_coverage) {
+                    mask[offset / 32] |= 1 << (offset % 32);
+                }
+            } else if (MP_OBJ_IS_TYPE(self->pixel_shader, &displayio_colorconverter_type)) {
+                if (!common_hal_displayio_colorconverter_convert(self->pixel_shader, value, pixel)) {
+                    // mark the pixel as transparent
+                    full_coverage = false;
+                } else if (!always_full_coverage) {
+                    mask[offset / 32] |= 1 << (offset % 32);
+                }
+            }
+        }
+    }
+
+    return full_coverage;
 }
 
 bool displayio_tilegrid_needs_refresh(displayio_tilegrid_t *self) {