instructions to use skia and glfw together. (download, installation, first program). works on Linux and Windows.

glfw_ship.cpp

/* Note: this Google copyright notice only applies to the original file, which has large sections copy-pasted here. my changes are under CC0 (public domain).

 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/*
this is intended as a second-resort, after trying to build using the official instructions inevitably fails because of poor documentation and strange build systems.
it documents a possible successful set of steps (the ones I took), but is just intended to be the shortest path to get a minimal setup running, not to be good or correct.

this was made by copy-pasting and fixing two sources: https://github.com/google/skia/tree/master/experimental/GLFWTest and https://gist.github.com/zester/5163313
don't bother trying these two sources; neither of them compiles on any system that has ever existed, because of typos.
I documented my steps below as I took them, but haven't run them through a second time to verify that they work. If someone succeeds with them, let me know!

step 1: install glfw (on Linux, probably just "sudo apt install libglfw3-dev" will get you an acceptable (and outdated) version. on Visual Studio 2017, you must build glfw from source, contrary to Internet claims that glfw's VS2015 pre-compiled version works.)
step 2: follow http://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html#_setting_up
step 3: if you're in Windows, you will need a copy of bash; cmd.exe will fail in a later step. on my system, a copy of bash came with my installation of Git for Windows.
step 4: follow https://skia.org/user/download, using the "Clone the Skia repository" section only. Use Bash, even if you're on Windows. the Windows check "where python" is useful because sometimes python ends up in stupid places for stupid reasons
step 5: go to https://skia.org/user/build and look at the instructions, but don't follow them.

Windows step 6, Visual Studio 2017:
here is where bash is required, because cmd.exe doesn't allow single quotes, which are necessary to give the VC path. the various skia_use_foo commands are necessary to stop VS from erroring out when the headers are missing
run these two commands, replacing "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC" with your own VC directory:
gn gen out/Static --args='is_official_build=true win_vc="C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC" skia_use_libpng=false skia_use_zlib=false skia_use_libwebp=false skia_enable_pdf=false skia_use_libjpeg_turbo=false skia_use_expat=false'
ninja -C out/Static

Windows step 7:
add this file to a new VS project
append "FOLDER1\skia\include\core;FOLDER1\skia\include\gpu;FOLDER1\skia\include\config;FOLDER1\skia\include\utils;FOLDER2\glfw\include'" to the VC include directories of your project, where FOLDERX represents the directories you put them in.
	you must include all 4 skia folders because the files inside skia folders assume they see the other folders.
	if you're unfamiliar with how the include directory works, it's in Project->Properties, VC++ Directories, Include Directories.
append "FOLDER1\skia\out\Static;FOLDER2\glfw\src\Debug;" to Library Directories, again replacing FOLDERX with the true location. add "opengl32.lib;skia.lib;glfw3.lib;" to Linker->Input->Additional Dependencies
Set build mode to x64.
Build! This will produce a debug mode binary.
If in the future you want a release mode binary, you will need to re-build glfw in release mode, and change the glfw library folder to FOLDER2\glfw\src\Release;

Linux step 6, Ubuntu 17.10. February 17, 2018:
you will need clang-6.0.
here's how: follow https://askubuntu.com/a/799998/. replace 3.9 by 6.0, and "xenial" by your distro
gcc-7.2, the default compiler on Ubuntu 17.10, does not work, because skia turned on Werror for release builds for some dumb reason.
don't do "sudo apt install clang", that won't work either. clang has problems with <stdafx.h>/<optional> depending on whether it uses libc++ or libstdc++, but I don't think clang-4.0, which is the package Ubuntu 17.10 uses, will work under any circumstance.
when getting 6.0 from the nightly packages, use "deb http://apt.llvm.org/artful/ llvm-toolchain-artful-6.0 main" and not "deb http://apt.llvm.org/artful/ llvm-toolchain-artful main", because llvm nightly's packaging is fucked up
ignore llvm's instructions on getting the nightly packages at https://apt.llvm.org/, they don't work.

Run:
sudo apt install libjpeg-dev libicu-dev libwebp-dev
bin/gn gen out/Static --args='is_official_build=true cc="clang-6.0" cxx="clang++-6.0"'

Linux step 7:
download this file as "glfw_ship.cpp". let "REPLACEME" be the folder your skia lives inside
g++ -g -std=c++1z glfw_ship.cpp -lskia -ldl -lpthread -ljpeg -lfreetype -lz -lpng -lglfw -lfontconfig -lwebp -lwebpmux -lwebpdemux -lGL -IREPLACEME/skia/include/gpu -IREPLACEME/skia/include/core -IREPLACEME/skia/include/config -IREPLACEME/skia/include/utils -LREPLACEME/skia/out/Static/
./a.out


eventually, you will want color-correct spaces, and there are 5 places below (Ctrl+F "enable correct color spaces"), where you should replace/uncomment lines to enable this.
warning: color-correct spaces don't work in VMWare, because mesa doesn't support it.
*/

#include "GLFW/glfw3.h"
#include "GrBackendSurface.h"
#include "GrContext.h"
#include "SkCanvas.h"
#include "SkColorSpace.h"
#include "SkSurface.h"
#include <stdio.h>
#include <stdlib.h>

//uncomment the two lines below to enable correct color spaces
//#define GL_FRAMEBUFFER_SRGB 0x8DB9
//#define GL_SRGB8_ALPHA8 0x8C43

GrContext* sContext = nullptr;
SkSurface* sSurface = nullptr;

void error_callback(int error, const char* description) {
	fputs(description, stderr);
}

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) {
	if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
		glfwSetWindowShouldClose(window, GL_TRUE);
}

void init_skia(int w, int h) {
	GrContextOptions options;
	options.fRequireDecodeDisableForSRGB = false;
	sContext = GrContext::MakeGL(nullptr, options).release();

	GrGLFramebufferInfo framebufferInfo;
	framebufferInfo.fFBOID = 0; // assume default framebuffer
	// We are always using OpenGL and we use RGBA8 internal format for both RGBA and BGRA configs in OpenGL.
	//(replace line below with this one to enable correct color spaces) framebufferInfo.fFormat = GL_SRGB8_ALPHA8;
	framebufferInfo.fFormat = GL_RGBA8;

	SkColorType colorType;
	if (kRGBA_8888_GrPixelConfig == kSkia8888_GrPixelConfig) {
		colorType = kRGBA_8888_SkColorType;
	}
	else {
		colorType = kBGRA_8888_SkColorType;
	}
	GrBackendRenderTarget backendRenderTarget(w, h,
		0, // sample count
		0, // stencil bits
		framebufferInfo);

	//(replace line below with this one to enable correct color spaces) sSurface = SkSurface::MakeFromBackendRenderTarget(sContext, backendRenderTarget, kBottomLeft_GrSurfaceOrigin, colorType, SkColorSpace::MakeSRGB(), nullptr).release();
	sSurface = SkSurface::MakeFromBackendRenderTarget(sContext, backendRenderTarget, kBottomLeft_GrSurfaceOrigin, colorType, nullptr, nullptr).release();
	if (sSurface == nullptr) abort();
}

void cleanup_skia() {
	delete sSurface;
	delete sContext;
}

const int kWidth = 960;
const int kHeight = 640;

int main(void) {
	GLFWwindow* window;
	glfwSetErrorCallback(error_callback);
	if (!glfwInit()) {
		exit(EXIT_FAILURE);
	}

	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	//(uncomment to enable correct color spaces) glfwWindowHint(GLFW_SRGB_CAPABLE, GL_TRUE);
	glfwWindowHint(GLFW_STENCIL_BITS, 0);
	//glfwWindowHint(GLFW_ALPHA_BITS, 0);
	glfwWindowHint(GLFW_DEPTH_BITS, 0);

	window = glfwCreateWindow(kWidth, kHeight, "Simple example", NULL, NULL);
	if (!window) {
		glfwTerminate();
		exit(EXIT_FAILURE);
	}
	glfwMakeContextCurrent(window);
	//(uncomment to enable correct color spaces) glEnable(GL_FRAMEBUFFER_SRGB);

	init_skia(kWidth, kHeight);

	glfwSwapInterval(1);
	glfwSetKeyCallback(window, key_callback);

	// Draw to the surface via its SkCanvas.
	SkCanvas* canvas = sSurface->getCanvas(); // We don't manage this pointer's lifetime.

	while (!glfwWindowShouldClose(window)) {
		glfwWaitEvents();
		SkPaint paint;
		paint.setColor(SK_ColorWHITE);
		canvas->drawPaint(paint);
		paint.setColor(SK_ColorBLUE);
		canvas->drawRect({100, 200, 300, 500}, paint);
		sContext->flush();

		glfwSwapBuffers(window);
	}

	cleanup_skia();

	glfwDestroyWindow(window);
	glfwTerminate();
	exit(EXIT_SUCCESS);
}