extend SkShader to report a luminance-color to be used for gamma correction

gm/aaclip.cpp

Index: gm/aaclip.cpp
diff --git a/gm/aaclip.cpp b/gm/aaclip.cpp
index 6419c8f989d98e72d802bd6fd2219be49513d4f9..b56ccd6a1c6af9e2e0ed6cbbad029af0a41e0062 100644
--- a/gm/aaclip.cpp
+++ b/gm/aaclip.cpp
@@ -9,6 +9,49 @@
 #include "SkCanvas.h"
 #include "SkPath.h"
 
+#include "SkGradientShader.h"
+static void set_gradient(SkPaint* paint) {
+    const SkPoint pts[] = { { 0, 0 }, { 240, 0 } };
+    SkColor colors[2];
+    colors[0] = paint->getColor();
+    colors[1] = SkColorSetA(colors[0], 0);
+    SkShader* shader = SkGradientShader::CreateLinear(pts, colors, NULL, 2, SkShader::kClamp_TileMode);
+    paint->setShader(shader)->unref();
+}
+
+static void set_face(SkPaint* paint) {
+    SkTypeface* face = SkTypeface::CreateFromName("serif", SkTypeface::kItalic);
+    SkSafeUnref(paint->setTypeface(face));
+}
+
+static void draw_pair(SkCanvas* canvas, SkPaint* paint) {
+    const char text[] = "Now is the time for all good";
+    const size_t len = strlen(text);
+
+    paint->setShader(NULL);
+    canvas->drawText(text, len, 10, 20, *paint);
+    set_gradient(paint);
+    canvas->drawText(text, len, 10, 40, *paint);
+}
+
+static void test_gamma(SkCanvas* canvas) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setLCDRenderText(true);
+    paint.setTextSize(18);
+    set_face(&paint);
+
+    draw_pair(canvas, &paint);
+    
+    canvas->translate(0, 50);
+    paint.setColor(SK_ColorRED);
+    draw_pair(canvas, &paint);
+    
+    canvas->translate(0, 50);
+    paint.setColor(SK_ColorBLUE);
+    draw_pair(canvas, &paint);
+}
+
 /** Draw a 2px border around the target, then red behind the target;
     set the clip to match the target, then draw >> the target in blue.
 */
@@ -80,6 +123,7 @@ protected:
     }
 
     virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        if (true) { test_gamma(canvas); return; }

[bungeman-skia, 2014/08/21 14:15:43]

I'm supposing this needs to be updated.

[reed1, 2014/08/21 20:07:38]

Done.

         // Initial pixel-boundary-aligned draw
         draw_rect_tests(canvas);