Add matrix operations to C canvas API

src/c/sk_surface.cpp

Index: src/c/sk_surface.cpp
diff --git a/src/c/sk_surface.cpp b/src/c/sk_surface.cpp
index c75ab23d55728f67ee0b348ba70bac82a3d24c65..7e93f9c7bd6f26520f6ec4e135c169fdac6b0786 100644
--- a/src/c/sk_surface.cpp
+++ b/src/c/sk_surface.cpp
@@ -91,6 +91,16 @@ static bool from_c_info(const sk_imageinfo_t& cinfo, SkImageInfo* info) {
     return true;
 }
 
+static void from_c_matrix(const sk_matrix_t* cmatrix, SkMatrix* matrix) {
+    if (cmatrix) {
+        matrix->setAll(cmatrix->mat[0], cmatrix->mat[1], cmatrix->mat[2],
+                       cmatrix->mat[3], cmatrix->mat[4], cmatrix->mat[5],
+                       cmatrix->mat[6], cmatrix->mat[7], cmatrix->mat[8]);
+    } else {
+        matrix->setIdentity();
+    }
+}
+
 const struct {
     sk_path_direction_t fC;
     SkPath::Direction   fSk;
@@ -320,6 +330,12 @@ void sk_canvas_skew(sk_canvas_t* ccanvas, float sx, float sy) {
     AsCanvas(ccanvas)->skew(sx, sy);
 }
 
+void sk_canvas_concat_matrix(sk_canvas_t* ccanvas, const sk_matrix_t* cmatrix) {
+    SkMatrix matrix;

[reed1, 2014/12/02 17:41:43]

can probably move the null-check to here, rather than in the converter (assuming
we want that and not to just crash/assert).

[abarth-chromium, 2014/12/02 17:43:16]

IMHO, we should crash/assert.  It seems better for the API to be strict, at
least at the beginning.  We can always loosen these things later, but they're
much harder to tighten.

+    from_c_matrix(cmatrix, &matrix);
+    AsCanvas(ccanvas)->concat(matrix);
+}
+
 void sk_canvas_draw_paint(sk_canvas_t* ccanvas, const sk_paint_t* cpaint) {
     AsCanvas(ccanvas)->drawPaint(AsPaint(*cpaint));
 }
@@ -419,13 +435,7 @@ sk_shader_t* sk_shader_new_linear_gradient(const sk_point_t pts[2],
         return NULL;
     }
     SkMatrix matrix;
-    if (cmatrix) {
-        matrix.setAll(cmatrix->mat[0], cmatrix->mat[1], cmatrix->mat[2],
-                      cmatrix->mat[3], cmatrix->mat[4], cmatrix->mat[5],
-                      cmatrix->mat[6], cmatrix->mat[7], cmatrix->mat[8]);
-    } else {
-        matrix.setIdentity();
-    }
+    from_c_matrix(cmatrix, &matrix);
     SkShader* s = SkGradientShader::CreateLinear(reinterpret_cast<const SkPoint*>(pts),
                                                  reinterpret_cast<const SkColor*>(colors),
                                                  colorPos, colorCount, mode, 0, &matrix);