camera: use slightly smaller scaled display image

Rather than use a half-sized image (which is slightly too large for the
display available) use an explicitly sized smaller image tile and crop
(do not copy) the data that would not be shown in any case.
NOTE: we still use a 2x scale factor.

main/camera.c

@@ -15,6 +15,12 @@
 // as we don't want the unit to shut down because of apparent inactivity.
 #define CAMERA_MIN_TIMEOUT_SECS 300
 
+// The image from the camera framebuffer is scaled and cropped to fit the display image
+// (Based on Jade screen dimensions and the fact that the image is half the screen.)
+#define DISPLAY_IMAGE_WIDTH 120
+#define DISPLAY_IMAGE_HEIGHT 135
+#define DISPLAY_IMAGE_SCALE_FACTOR 2
+
 void await_qr_help_activity(const char* url);
 
 gui_activity_t* make_camera_activity(const char* btnText, progress_bar_t* progress_bar, gui_view_node_t** image_node,
@@ -201,7 +207,7 @@ static void jade_camera_task(void* data)
     vTaskDelay(500 / portTICK_PERIOD_MS);
     void* image_buffer = NULL;
     Picture pic = {};
-    const size_t image_size = sizeof(uint8_t[CAMERA_IMAGE_WIDTH / 2][CAMERA_IMAGE_HEIGHT / 2]);
+    const size_t image_size = sizeof(uint8_t[DISPLAY_IMAGE_HEIGHT][DISPLAY_IMAGE_WIDTH]);
     wait_event_data_t* event_data = NULL;
     if (has_gui) {
         // Update the text label to indicate readiness
@@ -213,9 +219,8 @@ static void jade_camera_task(void* data)
         // captures potentially sensitive data eg. a valid mnemonic qrcode.
         image_buffer = JADE_MALLOC_PREFER_SPIRAM(image_size);
         SENSITIVE_PUSH(image_buffer, image_size);
-        // NOTE rotated so height <-> width
-        pic.width = CAMERA_IMAGE_HEIGHT / 2;
-        pic.height = CAMERA_IMAGE_WIDTH / 2;
+        pic.width = DISPLAY_IMAGE_WIDTH;
+        pic.height = DISPLAY_IMAGE_HEIGHT;
         pic.bytes_per_pixel = 1;
         pic.data_8 = image_buffer;
 
@@ -243,20 +248,22 @@ static void jade_camera_task(void* data)
         // If we have a gui, update the image on screen and check for button events
         if (has_gui) {
             // Copy from camera output to screen image
-            JADE_ASSERT(fb->len == 4 * image_size); // twice width and twice height
-            uint8_t(*scale_rotated)[CAMERA_IMAGE_HEIGHT / 2] = image_buffer;
-            uint8_t(*buf_as_matrix)[CAMERA_IMAGE_WIDTH] = (uint8_t(*)[CAMERA_IMAGE_WIDTH])fb->buf;
-            for (size_t x = 0; x < CAMERA_IMAGE_WIDTH / 2; ++x) {
-                for (size_t y = 0; y < CAMERA_IMAGE_HEIGHT / 2; ++y) {
+            // (Ensure source image large enough to be scaled down to display image size)
+            const uint8_t scale = DISPLAY_IMAGE_SCALE_FACTOR;
+            JADE_ASSERT(fb->len >= scale * scale * image_size);
+            uint8_t(*image_matrix)[DISPLAY_IMAGE_WIDTH] = image_buffer;
+            uint8_t(*fb_matrix)[CAMERA_IMAGE_WIDTH] = (uint8_t(*)[CAMERA_IMAGE_WIDTH])fb->buf;
+            for (size_t imgy = 0; imgy < DISPLAY_IMAGE_HEIGHT; ++imgy) {
+                for (size_t imgx = 0; imgx < DISPLAY_IMAGE_WIDTH; ++imgx) {
 #if defined(CONFIG_CAMERA_ROTATE_90)
-                    scale_rotated[x][y] = buf_as_matrix[(CAMERA_IMAGE_HEIGHT - 1) - (y * 2)][x * 2];
+                    image_matrix[imgy][imgx] = fb_matrix[(CAMERA_IMAGE_HEIGHT - 1) - (imgx * scale)][imgy * scale];
 #elif defined(CONFIG_CAMERA_ROTATE_180)
-                    scale_rotated[x][y]
-                        = buf_as_matrix[(CAMERA_IMAGE_WIDTH - 1) - (x * 2)][(CAMERA_IMAGE_HEIGHT - 1) - (y * 2)];
+                    image_matrix[imgy][imgx] = fb_matrix[(CAMERA_IMAGE_WIDTH - 1) - (imgy * scale)]
+                                                        [(CAMERA_IMAGE_HEIGHT - 1) - (imgx * scale)];
 #elif defined(CONFIG_CAMERA_ROTATE_270)
-                    scale_rotated[x][y] = buf_as_matrix[y * 2][(CAMERA_IMAGE_WIDTH - 1) - (x * 2)];
+                    image_matrix[imgy][imgx] = fb_matrix[imgx * scale][(CAMERA_IMAGE_WIDTH - 1) - (imgy * scale)];
 #else
-                    scale_rotated[x][y] = buf_as_matrix[x * 2][y * 2];
+                    image_matrix[imgy][imgx] = fb_matrix[imgy * scale][imgx * scale];
 #endif
                 }
             }