Add Atlas Text interface for rendering SDF glyphs.

This new API is built upon SDF text atlas code from the GPU backend. Unlike using the GPU
backend to draw text, this set of interfaces allows the client to render the SDF glyphs. The
client issues text draws to potentially multiple targets and then the client flushes. The
client then gets commands from Skia with data to put into a texture atlas and vertices to
draw that reference the texture. The client is responsible for creating the texture, uploading
the SDF data to the texture, and drawing the vertices provided by Skia.

Change-Id: Ie9447e19b85f0ce1c2b942e5216c787a74f335d3
Reviewed-on: https://skia-review.googlesource.com/59360
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/include/atlastext/SkAtlasTextTarget.h b/include/atlastext/SkAtlasTextTarget.h
new file mode 100644
index 0000000000..0859afde39
--- /dev/null
+++ b/include/atlastext/SkAtlasTextTarget.h
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkAtlasTextTarget_DEFINED
+#define SkAtlasTextTarget_DEFINED
+
+#include <memory>
+#include "SkRefCnt.h"
+#include "SkScalar.h"
+
+class SkAtlasTextContext;
+class SkAtlasTextFont;
+
+/** Represents a client-created renderable surface and is used to draw text into the surface. */
+class SK_API SkAtlasTextTarget {
+public:
+    virtual ~SkAtlasTextTarget();
+
+    /**
+     * Creates a text drawing target. ‘handle’ is used to identify this rendering surface when
+     * draws are flushed to the SkAtlasTextContext's SkAtlasTextRenderer.
+     */
+    static std::unique_ptr<SkAtlasTextTarget> Make(sk_sp<SkAtlasTextContext>, int width, int height,
+                                                   void* handle);
+
+    /**
+     * Enqueues a text draw in the target. The meaning of 'color' here is interpreted by the
+     * client's SkAtlasTextRenderer when it actually renders the text.
+     */
+    virtual void drawText(const void* text, size_t byteLength, SkScalar x, SkScalar y,
+                          uint32_t color, const SkAtlasTextFont& font) = 0;
+
+    /** Issues all queued text draws to SkAtlasTextRenderer. */
+    virtual void flush() = 0;
+
+    int width() const { return fWidth; }
+    int height() const { return fHeight; }
+
+    void* handle() const { return fHandle; }
+
+    SkAtlasTextContext* context() const { return fContext.get(); }
+
+protected:
+    SkAtlasTextTarget(sk_sp<SkAtlasTextContext>, int width, int height, void* handle);
+
+    void* const fHandle;
+    const sk_sp<SkAtlasTextContext> fContext;
+    const int fWidth;
+    const int fHeight;
+
+private:
+    SkAtlasTextTarget() = delete;
+    SkAtlasTextTarget(const SkAtlasTextContext&) = delete;
+    SkAtlasTextTarget& operator=(const SkAtlasTextContext&) = delete;
+};
+
+#endif