Add sw support to viewer on Linux.

tools/viewer/sk_app/unix/RasterWindowContext_unix.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "RasterWindowContext_unix.h"
+
+#include "SkSurface.h"
+#include "SkTypes.h"
+
+using ::Window;
+
+namespace sk_app {
+
+RasterWindowContext* RasterWindowContext_unix::Create(Display* display, Window window,
+                                                      const DisplayParams& params) {
+    RasterWindowContext* ctx = new RasterWindowContext_unix(display, window, params);
+    if (!ctx->isValid()) {
+        delete ctx;
+        ctx = nullptr;
+    }
+    return ctx;
+}
+
+RasterWindowContext_unix::RasterWindowContext_unix(Display* display, Window window,
+                                                   const DisplayParams& params)
+        : fDisplay(display)
+        , fWindow(window) {
+    fDisplayParams = params;
+    XWindowAttributes attrs;
+    XGetWindowAttributes(fDisplay, fWindow, &attrs);
+    fGC = XCreateGC(fDisplay, fWindow, 0, nullptr);
+    this->resize(attrs.width, attrs.height);
+}
+
+void RasterWindowContext_unix::setDisplayParams(const DisplayParams& params) {
+    fDisplayParams = params;
+    XWindowAttributes attrs;
+    XGetWindowAttributes(fDisplay, fWindow, &attrs);
+    this->resize(attrs.width, attrs.height);
+}
+
+void RasterWindowContext_unix::resize(uint32_t w, uint32_t h) {
+    SkImageInfo info = SkImageInfo::Make(w, h, fDisplayParams.fColorType, kPremul_SkAlphaType,
+                                         fDisplayParams.fColorSpace);
+    fBackbufferSurface = SkSurface::MakeRaster(info);
+
+}
+
+sk_sp<SkSurface> RasterWindowContext_unix::getBackbufferSurface() { return fBackbufferSurface; }
+
+void RasterWindowContext_unix::swapBuffers() {
+    SkPixmap pm;
+    if (!fBackbufferSurface->peekPixels(&pm)) {
+        return;
+    }
+    int bitsPerPixel = pm.info().bytesPerPixel() * 8;
+    XImage image;
+    image.width = pm.width();
+    image.height = pm.height();
+    image.format = ZPixmap;
+    image.data = (char*) pm.addr();
+    image.byte_order = LSBFirst;
+    image.bitmap_unit = bitsPerPixel;
+    image.bitmap_bit_order = LSBFirst;
+    image.bitmap_pad = bitsPerPixel;
+    image.depth = 24;
+    image.bytes_per_line = pm.rowBytes() - pm.width() * pm.info().bytesPerPixel();
+    image.bits_per_pixel = bitsPerPixel;
+    if (!XInitImage(&image)) {
+        return;
+    }
+    XPutImage(fDisplay, fWindow, fGC, &image, 0, 0, 0, 0, pm.width(), pm.height());
+}
+
+}   // namespace sk_app