text: /*
   * Copyright 2013 Google Inc.
   *
   * Use of this source code is governed by a BSD-style license that can be
   * found in the LICENSE file.
   */
  
  #include "gm.h"
  #include "sk_tool_utils.h"
  #include "SkBlendModePriv.h"
  #include "SkCanvas.h"
  #include "SkGradientShader.h"
  #include "SkLumaColorFilter.h"
  
  static SkScalar kSize   = 80;
  static SkScalar kInset  = 10;
  static SkColor  kColor1 = SkColorSetARGB(0xff, 0xff, 0xff, 0);
  static SkColor  kColor2 = SkColorSetARGB(0xff, 0x82, 0xff, 0);
  
  static void draw_label(SkCanvas* canvas, const char* label,
                         const SkPoint& offset) {
      SkFont font(sk_tool_utils::create_portable_typeface());
      font.setEdging(SkFont::Edging::kAlias);
  
      size_t len = strlen(label);
  
      SkScalar width = font.measureText(label, len, kUTF8_SkTextEncoding);
      canvas->drawSimpleText(label, len, kUTF8_SkTextEncoding, offset.x() - width / 2, offset.y(),
                             font, SkPaint());
  }
  
  static void draw_scene(SkCanvas* canvas, const sk_sp<SkColorFilter>& filter, SkBlendMode mode,
                         const sk_sp<SkShader>& s1, const sk_sp<SkShader>& s2) {
      SkPaint paint;
      paint.setAntiAlias(true);
      SkRect r, c, bounds = SkRect::MakeWH(kSize, kSize);
  
      c = bounds;
      c.fRight = bounds.centerX();
      paint.setARGB(0x20, 0, 0, 0xff);
      canvas->drawRect(bounds, paint);
  
      canvas->saveLayer(&bounds, nullptr);
  
      r = bounds;
      r.inset(kInset, 0);
      paint.setShader(s1);
      paint.setColor(s1 ? SK_ColorBLACK : SkColorSetA(kColor1, 0x80));
      canvas->drawOval(r, paint);
      if (!s1) {
          canvas->save();
          canvas->clipRect(c);
          paint.setColor(kColor1);
          canvas->drawOval(r, paint);
          canvas->restore();
      }
  
      SkPaint xferPaint;
      xferPaint.setBlendMode(mode);
      canvas->saveLayer(&bounds, &xferPaint);
  
      r = bounds;
      r.inset(0, kInset);
      paint.setShader(s2);
      paint.setColor(s2 ? SK_ColorBLACK : SkColorSetA(kColor2, 0x80));
      paint.setColorFilter(filter);
      canvas->drawOval(r, paint);
      if (!s2) {
          canvas->save();
          canvas->clipRect(c);
          paint.setColor(kColor2);
          canvas->drawOval(r, paint);
          canvas->restore();
      }
  
      canvas->restore();
      canvas->restore();
  }
  
  class LumaFilterGM : public skiagm::GM {
  public:
      LumaFilterGM() {
          SkColor  g1Colors[] = { kColor1, SkColorSetA(kColor1, 0x20) };
          SkColor  g2Colors[] = { kColor2, SkColorSetA(kColor2, 0x20) };
          SkPoint  g1Points[] = { { 0, 0 }, { 0,     100 } };
          SkPoint  g2Points[] = { { 0, 0 }, { kSize, 0   } };
          SkScalar pos[] = { 0.2f, 1.0f };
  
          fFilter = SkLumaColorFilter::Make();
          fGr1 = SkGradientShader::MakeLinear(g1Points, g1Colors, pos, SK_ARRAY_COUNT(g1Colors),
                                              SkShader::kClamp_TileMode);
          fGr2 = SkGradientShader::MakeLinear(g2Points, g2Colors, pos, SK_ARRAY_COUNT(g2Colors),
                                              SkShader::kClamp_TileMode);
      }
  
  protected:
  
      SkString onShortName() override {
          return SkString("lumafilter");
      }
  
      SkISize onISize() override {
          return SkISize::Make(600, 420);
      }
  
      void onDraw(SkCanvas* canvas) override {
          SkBlendMode modes[] = {
              SkBlendMode::kSrcOver,
              SkBlendMode::kDstOver,
              SkBlendMode::kSrcATop,
              SkBlendMode::kDstATop,
              SkBlendMode::kSrcIn,
              SkBlendMode::kDstIn,
          };
          struct {
              const sk_sp<SkShader>& fShader1;
              const sk_sp<SkShader>& fShader2;
          } shaders[] = {
              { nullptr, nullptr },
              { nullptr, fGr2 },
              { fGr1, nullptr },
              { fGr1, fGr2 },
          };
  
          SkScalar gridStep = kSize + 2 * kInset;
          for (size_t i = 0; i < SK_ARRAY_COUNT(modes); ++i) {
              draw_label(canvas, SkBlendMode_Name(modes[i]),
                         SkPoint::Make(gridStep * (0.5f + i), 20));
          }
  
          for (size_t i = 0; i < SK_ARRAY_COUNT(shaders); ++i) {
              canvas->save();
              canvas->translate(kInset, gridStep * i + 30);
              for (size_t m = 0; m < SK_ARRAY_COUNT(modes); ++m) {
                  draw_scene(canvas, fFilter, modes[m], shaders[i].fShader1,
                             shaders[i].fShader2);
                  canvas->translate(gridStep, 0);
              }
              canvas->restore();
          }
      }
  
  private:
      sk_sp<SkColorFilter>    fFilter;
      sk_sp<SkShader>         fGr1, fGr2;
  
      typedef skiagm::GM INHERITED;
  };
  
  //////////////////////////////////////////////////////////////////////////////
  
  DEF_GM(return new LumaFilterGM;)
  