I've successfully created a set of core, display driver, and project config libraries for an SSD1351 OLED display (adafruit's breakout board).

How it works:

• uGFX is added in arduino's library folder. It doesn't work as an arduino library, though, but there's a wrapper for that.
• ugfx-arduino is a simple library that includes ugfx's single-file-source and the main header (gfx.h). gfx.h is found in the ugfx directory, so arduino will add that to the compiler's include path. We can exploit this to include src/gfx_mk.c, which is the one file we need to compile to use ugfx.
• ugfx-arduino-ssd1351 is a driver library that has two interfaces: one for ugfx and one for the actual application: pin numbers must be set, and they should not be picked by the driver, but by the application.
• teensy3.1-ssd1351-ugfx-config is the project-specific library that configures ugfx and the driver for a specific sketch.

I have not yet found a way of getting rid of the config library, but I think that's not too bad.

So let's sum it up!

ugfx-arduino

The wrapper around ugfx, to make the include path and core available.

<sketchbook>/libraries/ugfx-arduino/ugfx-arduino.h:

#ifndef UGFX_ARDUINO_H
#define UGFX_ARDUINO_H

#include <gfx.h>

#endif // UGFX_ARDUINO_H

#include "src/gfx_mk.c"

ugfx-arduino-ssd1351

A driver I adapted from the ugfx sources. I'll not include the code here because it's simply too much, but this is the place where ugfx is told about the driver's features in gdisp_lld_config.h:

<sketchbook>/libraries/ugfx-arduino-ssd1351/
.
├── board_SSD1351.cpp
├── board_SSD1351.h
├── gdisp_lld_config.h
├── gdisp_lld_SSD1351.c
├── SSD1351.h
└── ugfx-arduino-ssd1351.h

teensy3.1-ssd1351-ugfx-config

#ifndef _GFXCONF_H
#define _GFXCONF_H

/* The operating system to use. One of these must be defined - preferably in your Makefile */
//#define GFX_USE_OS_CHIBIOS	FALSE
//#define GFX_USE_OS_WIN32		FALSE
//#define GFX_USE_OS_LINUX		FALSE
//#define GFX_USE_OS_OSX		FALSE
#define GFX_USE_OS_ARDUINO      TRUE
//#define GFX_USE_OS_RAW32 TRUE

/* GFX sub-systems to turn on */
#define GFX_USE_GDISP			TRUE

/* Features for the GDISP sub-system. */
#define GDISP_NEED_VALIDATION	TRUE
#define GDISP_NEED_CLIP			TRUE

#endif /* _GFXCONF_H */

#ifndef UGFX_ARDUINO_SSD1351_PINS_H
#define UGFX_ARDUINO_SSD1351_PINS_H

#define GPIO_DC    16
#define GPIO_RESET 15
#define GPIO_CS    14

#endif // UGFX_ARDUINO_SSD1351_PINS_H

#ifndef TEENSY31_SSD1351_UGFX_CONFIG_H
#define TEENSY31_SSD1351_UGFX_CONFIG_H

#include <ugfx-arduino.h> // main library
#include <ugfx-arduino-ssd1351.h> // display driver library

#endif // TEENSY31_SSD1351_UGFX_CONFIG_H

Sketch

#include <teensy3.1-ssd1351-ugfx-config.h>
#include <SPI.h>

void setup() {
  coord_t    width, height;
  coord_t   i, j;

  SPI.begin();

  // Initialize and clear the display
  gfxInit();

  // Get the screen size
  width = gdispGetWidth();
  height = gdispGetHeight();

  // Code Here
  gdispDrawBox(10, 10, width / 2, height / 2, Yellow);
  gdispFillArea(width / 2, height / 2, width / 2 - 10, height / 2 - 10, Blue);
  gdispDrawLine(5, 30, width - 50, height - 40, Red);

  for (i = 5, j = 0; i < width && j < height; i += 7, j += i / 20)
    gdispDrawPixel(i, j, White);

  SPI.end();
}

void loop() {
}