am7xxx: add am7xxx_calc_scaled_image_dimensions()

This function is useful to calculate the dimensions of an image which
will be sent with am7xxx_send_image() in a way that keeps the original
image aspect ratio.

diff --git a/src/am7xxx.c b/src/am7xxx.c
index f04b638..a840589 100644 (file)
--- a/src/am7xxx.c
+++ b/src/am7xxx.c
@@ -690,6 +690,68 @@ int am7xxx_get_device_info(am7xxx_device *dev,
        return 0;
 }
 
+int am7xxx_calc_scaled_image_dimensions(am7xxx_device *dev,
+                                       unsigned int upscale,
+                                       unsigned int original_width,
+                                       unsigned int original_height,
+                                       unsigned int *scaled_width,
+                                       unsigned int *scaled_height)
+{
+
+       am7xxx_device_info device_info;
+       float width_ratio;
+       float height_ratio;
+       int ret;
+
+       ret = am7xxx_get_device_info(dev, &device_info);
+       if (ret < 0) {
+               error(dev->ctx, "cannot get device info\n");
+               return ret;
+       }
+
+       /*
+        * Check if we need to rescale; if the input image fits the native
+        * dimensions there is no need to, unless we want to upscale.
+        */
+       if (!upscale &&
+           original_width <= device_info.native_width &&
+           original_height <= device_info.native_height ) {
+               debug(dev->ctx, "CASE 0, no rescaling, the original image fits already\n");
+               *scaled_width = original_width;
+               *scaled_height = original_height;
+               return 0;
+       }
+
+       /* Input dimensions relative to the device native dimensions */
+       width_ratio =  (float)original_width / device_info.native_width;
+       height_ratio = (float)original_height / device_info.native_height;
+
+       if (width_ratio > height_ratio) {
+               /*
+                * The input is proportionally "wider" than the device viewport
+                * so it's height needs to be adjusted
+                */
+               debug(dev->ctx, "CASE 1, original image wider, adjust the scaled height\n");
+               *scaled_width = device_info.native_width;
+               *scaled_height = (unsigned int)(original_height / width_ratio);
+       } else if (width_ratio < height_ratio) {
+               /*
+                * The input is proportionally "taller" than the device viewport
+                * so its width needs to be adjusted
+                */
+               debug(dev->ctx, "CASE 2 original image taller, adjust the scaled width\n");
+               *scaled_width = (unsigned int)(original_width / height_ratio);
+               *scaled_height = device_info.native_height;
+       } else {
+               debug(dev->ctx, "CASE 3, just rescale, same aspect ratio already\n");
+               *scaled_width = device_info.native_width;
+               *scaled_height = device_info.native_height;
+       }
+       debug(dev->ctx, "scaled dimensions: %dx%d\n", *scaled_width, *scaled_height);
+
+       return 0;
+}
+
 int am7xxx_send_image(am7xxx_device *dev,
                      am7xxx_image_format format,
                      unsigned int width,

diff --git a/src/am7xxx.h b/src/am7xxx.h
index 4fe9b00..79d960a 100644 (file)
--- a/src/am7xxx.h
+++ b/src/am7xxx.h
@@ -179,6 +179,28 @@ int am7xxx_get_device_info(am7xxx_device *dev,
                           am7xxx_device_info *device_info);
 
 /**
+ * Calculate the dimensions of an image to be shown on an am7xxx device.
+ *
+ * Before sending images bigger than the device native dimensions the user
+ * needs to rescale them, this utility function does the calculation in a way
+ * that the original image aspect ratio is preserved.
+ * 
+ * @param[in] dev A pointer to the structure representing the device to get info of
+ * @param[in] upscale Whether to calculate scaled dimensions for images smaller than the native dimesions
+ * @param[in] original_width The width of the original image
+ * @param[in] original_height The height of the original image
+ * @param[out] scaled_width The width the rescaled image should have
+ * @param[out] scaled_height The height the rescaled image should have
+ *
+ * @return 0 on success, a negative value on error
+ */
+int am7xxx_calc_scaled_image_dimensions(am7xxx_device *dev,
+                                       unsigned int upscale,
+                                       unsigned int original_width,
+                                       unsigned int original_height,
+                                       unsigned int *scaled_width,
+                                       unsigned int *scaled_height);
+/**
  * Send an image for display on a am7xxx device.
  *
  * This is the function that actually makes the device display something.