Add an example showing how to use the Pathfinder C API with GLFW

Closes #258.

.gitignore

@@ -6,6 +6,7 @@ target
 /site/dist
 node_modules
 /examples/c_canvas_minimal/build
+/examples/c_canvas_glfw_minimal/build
 /shaders/build
 /c/build
 /examples/macos_app/Pathfinder\ Example.xcodeproj/project.xcworkspace/xcuserdata/*

c/cbindgen.toml

@@ -5,17 +5,15 @@ header = """\
 #ifndef PF_PATHFINDER_H
 #define PF_PATHFINDER_H
 
-#ifdef __APPLE__
+#if defined(__APPLE__) && defined(__OBJC__)
 #include <QuartzCore/QuartzCore.h>
+#else
+typedef struct CAMetalLayerPrivate CAMetalLayer;
 #endif
 
 #ifdef __cplusplus
 extern \"C\" {
 #endif
-
-#ifndef __APPLE__
-typedef struct CAMetalLayerPrivate CAMetalLayer;
-#endif
 """
 trailer = """\
 #ifdef __cplusplus

examples/c_canvas_glfw_minimal/Makefile

@@ -0,0 +1,47 @@
+OBJ_DIR?=build
+TARGET_DIR?=build
+SRC_DIR?=.
+RUST_TARGET_DIR?=../../target
+RUST_SRC_DIR?=../../c
+RUSTFLAGS?=
+
+CFLAGS?=-Wall -g -I../../c/build/include
+LIBS?=-lpathfinder_c -lglfw
+MKDIR?=mkdir -p
+RM?=rm
+CARGO?=cargo
+
+UNAME=$(shell uname -s)
+ifeq ($(UNAME),Darwin)
+	# FIXME(pcwalton): Don't link against HarfBuzz!!
+	LIBS+=-framework OpenGL -framework CoreFoundation -framework CoreGraphics -framework CoreText
+	LIBS+=-framework Metal -lharfbuzz
+else
+	LIBS+=-lGL
+endif
+
+ifeq ($(DEBUG),)
+	CFLAGS+=-O2
+	LDFLAGS?=-L$(RUST_TARGET_DIR)/release
+	CARGOFLAGS?=--release
+else
+	CFLAGS+=-O0
+	LDFLAGS?=-L$(RUST_TARGET_DIR)/debug
+	CARGOFLAGS?=
+endif
+
+all:	$(TARGET_DIR)/c_canvas_glfw_minimal
+
+.PHONY:	clean rustlib
+
+$(TARGET_DIR)/c_canvas_glfw_minimal:	$(OBJ_DIR)/c_canvas_glfw_minimal.o rustlib
+	$(MKDIR) $(TARGET_DIR) && $(CC) $(LDFLAGS) $(LIBS) -o $@ $<
+
+$(OBJ_DIR)/%.o:	$(SRC_DIR)/%.c
+	$(MKDIR) $(OBJ_DIR) && $(CC) -c $(CFLAGS) -o $@ $<
+
+rustlib:
+	cd $(RUST_SRC_DIR) && RUSTFLAGS="$(RUSTFLAGS)" $(CARGO) build $(CARGOFLAGS)
+
+clean:
+	$(RM) -rf $(TARGET_DIR) && $(RM) -rf $(OBJ_DIR)

examples/c_canvas_glfw_minimal/c_canvas_glfw_minimal.c

@@ -0,0 +1,100 @@
+// pathfinder/examples/c_canvas_glfw_minimal/c_canvas_glfw_minimal.c
+//
+// Copyright © 2019 The Pathfinder Project Developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#include <GLFW/glfw3.h>
+#include <pathfinder/pathfinder.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static void HandleGLFWError(int errorCode, const char *description);
+static const void *LoadGLFunction(const char *name, void *userdata);
+static void HandleKeypress(GLFWwindow *window, int key, int scancode, int action, int mods);
+
+int main(int argc, const char **argv) {
+    // Set up GLFW.
+    GLFWwindow *window;
+    if (!glfwInit())
+        return 1;
+    glfwSetErrorCallback(HandleGLFWError);
+
+    // Make sure we have at least a GL 3.0 context. Pathfinder requires this.
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);
+
+    // Open a window.
+    window = glfwCreateWindow(640, 480, "Minimal canvas example (GLFW/C API)", NULL, NULL);
+
+    // Make the OpenGL context current.
+    glfwMakeContextCurrent(window);
+
+    // Create a Pathfinder renderer.
+    PFGLLoadWith(LoadGLFunction, NULL);
+    PFGLDestFramebufferRef dest_framebuffer =
+        PFGLDestFramebufferCreateFullWindow(&(PFVector2I){640, 480});
+    PFGLRendererRef renderer = PFGLRendererCreate(PFGLDeviceCreate(PF_GL_VERSION_GL3, 0),
+                                                  PFFilesystemResourceLoaderLocate(),
+                                                  dest_framebuffer,
+                                                  &(PFRendererOptions){
+        (PFColorF){1.0, 1.0, 1.0, 1.0}, PF_RENDERER_OPTIONS_FLAGS_HAS_BACKGROUND_COLOR
+    });
+
+    // Make a canvas. We're going to draw a house.
+    PFCanvasRef canvas = PFCanvasCreate(PFCanvasFontContextCreateWithSystemSource(),
+                                        &(PFVector2F){640.0f, 480.0f});
+
+    // Set line width.
+    PFCanvasSetLineWidth(canvas, 10.0f);
+
+    // Draw walls.
+    PFCanvasStrokeRect(canvas, &(PFRectF){{75.0f, 140.0f}, {225.0f, 250.0f}});
+
+    // Draw door.
+    PFCanvasFillRect(canvas, &(PFRectF){{130.0f, 190.0f}, {170.0f, 250.0f}});
+
+    // Draw roof.
+    PFPathRef path = PFPathCreate();
+    PFPathMoveTo(path, &(PFVector2F){50.0, 140.0});
+    PFPathLineTo(path, &(PFVector2F){150.0, 60.0});
+    PFPathLineTo(path, &(PFVector2F){250.0, 140.0});
+    PFPathClosePath(path);
+    PFCanvasStrokePath(canvas, path);
+
+    // Render the canvas to screen.
+    PFSceneRef scene = PFCanvasCreateScene(canvas);
+    PFSceneProxyRef scene_proxy = PFSceneProxyCreateFromSceneAndRayonExecutor(scene);
+    PFSceneProxyBuildAndRenderGL(scene_proxy, renderer, PFBuildOptionsCreate());
+    glfwSwapBuffers(window);
+
+    // Wait for a keypress.
+    glfwSetKeyCallback(window, HandleKeypress);
+    while (!glfwWindowShouldClose(window))
+        glfwPollEvents();
+
+    // Finish up.
+    glfwTerminate();
+    return 0;
+}
+
+static void HandleGLFWError(int errorCode, const char *description) {
+    fprintf(stderr, "GLFW error: %s [%d]\n", description, errorCode);
+    exit(1);
+}
+
+static void HandleKeypress(GLFWwindow *window, int key, int scancode, int action, int mods) {
+    glfwSetWindowShouldClose(window, GLFW_TRUE);
+}
+
+static const void *LoadGLFunction(const char *name, void *userdata) {
+    return glfwGetProcAddress(name);
+}