A small compatible gpu
For the purpose described, you can dispense with an intermediary Raspberry Pi or Arduino module: The simplest and possibly least expensive application would be a USB touchscreen graphic module, such as those from Robopeak. 



This is an open source hardware design, available from the usual online sources such as eBay (~ US$43+shipping).

There are similar or even much more capable displays if you search on sites like DigiKey for USB color graphic display modules. For instance, the FTDi VM800BU (datasheet link) sells for US$69 in single units.



These modules incorporate a graphics processor and requisite hardware and software, including an ARM or similar processor, on board. This simplifies the interfacing from the PC to a simple USB data stream - simpler yet if a device driver is available for your operating system of choice.