During the media mini-summit I went through all 8 combinations of cropping, composing and scaling (i.e. none of these features is present, or only cropping, only composing, etc.). In particular I showed what I thought should happen if you change a crop rectangle, compose rectangle or the format rectangle (VIDIOC_S_FMT). In my proposal the format rectangle would increase in size if you attempt to set the compose rectangle wholly or partially outside the current format rectangle. Most (all?) of the developers present didn't like that and I was asked to take another look at that. After looking at this some more I realized that there was no need for this and it is OK to constrain a compose rectangle to the current format rectangle. All you need to do if you want to place the compose rectangle outside of the format rectangle is to just change the format rectangle first. If the driver supports composition then increasing the format rectangle will not change anything else, so that is a safe operation without side-effects. However, changing the crop rectangle *can* change the format rectangle. In the simple case of hardware that just supports cropping this is obvious, since the crop and format rectangles must always be of the same size, so changing one will change the other. But if you throw in a scaler as well, you usually still have such constraints based on the scaler capabilities. So assuming a scaler that can only scale 4 times (or less) up or down in each direction, then setting a crop rectangle of 240x160 will require that the format rectangle has a width in the range of 240/4 - 240*4 (60-960) and a height in the range of 160/4 - 160*4 (40-640). Anything outside of that will have to be corrected. In my opinion this is valid behavior, and the specification also clearly specifies in the VIDIOC_S_CROP and VIDIOC_S_SELECTION documentation that the format may change after changing the crop rectangle. Note that for output streams the role of crop and compose is swapped. So for output streams it is the crop rectangle that will always be constrained by the format rectangle, and it is the compose rectangle that might change the format rectangle based on scaler constraints. I think this makes sense and unless there are comments this is what I plan to implement in my vivi rewrite which supports all these crop/compose/scale combinations. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
