[cairo-spans] New abstract types for scan converting polygons.

A cairo_span_renderer_t implementation can be provided by a surface if
it wants to render paths as horizontal spans of the alpha component of
a mask.  Its job is to composite a source pattern to the destination
surface when given spans of alpha coverage for a row while taking care
of backend specific clipping.

A cairo_scan_converter_t takes edges of a flattened path and generates
spans for a span renderer to render.

1 files changed, 124 insertions, 0 deletions

diff --git a/src/cairo-spans-private.h b/src/cairo-spans-private.h
new file mode 100644
index 000000000..ba10d5b26
--- /dev/null
+++ b/src/cairo-spans-private.h
@@ -0,0 +1,124 @@
+/* -*- Mode: c; tab-width: 8; c-basic-offset: 4; indent-tabs-mode: t; -*- */
+/* cairo - a vector graphics library with display and print output
+ *
+ * Copyright (c) 2008  M Joonas Pihlaja
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+#ifndef CAIRO_SPANS_PRIVATE_H
+#define CAIRO_SPANS_PRIVATE_H
+#include "cairo-types-private.h"
+#include "cairo-compiler-private.h"
+
+/* Number of bits of precision used for alpha. */
+#define CAIRO_SPANS_UNIT_COVERAGE_BITS 8
+#define CAIRO_SPANS_UNIT_COVERAGE ((1 << CAIRO_SPANS_UNIT_COVERAGE_BITS)-1)
+
+/* A structure representing an open-ended horizontal span of constant
+ * pixel coverage. */
+typedef struct _cairo_half_open_span {
+    /* The inclusive x-coordinate of the start of the span. */
+    int x;
+
+    /* The pixel coverage for the pixels to the right. */
+    int coverage;
+} cairo_half_open_span_t;
+
+/* Span renderer interface. Instances of renderers are provided by
+ * surfaces if they want to composite spans instead of trapezoids. */
+typedef struct _cairo_span_renderer cairo_span_renderer_t;
+struct _cairo_span_renderer {
+    /* Called to destroy the renderer. */
+    cairo_destroy_func_t	destroy;
+
+    /* Render the spans on row y of the source by whatever compositing
+     * method is required.  The function should ignore spans outside
+     * the bounding box set by the init() function. */
+    cairo_status_t (*render_row)(
+	void				*abstract_renderer,
+	int				 y,
+	const cairo_half_open_span_t	*coverages,
+	unsigned			 num_coverages);
+
+    /* Called after all rows have been rendered to perform whatever
+     * final rendering step is required.  This function is called just
+     * once before the renderer is destroyed. */
+    cairo_status_t (*finish)(
+	void		      *abstract_renderer);
+
+    /* Private status variable. */
+    cairo_status_t status;
+};
+
+/* Scan converter interface. */
+typedef struct _cairo_scan_converter cairo_scan_converter_t;
+struct _cairo_scan_converter {
+    /* Destroy this scan converter. */
+    cairo_destroy_func_t	destroy;
+
+    /* Add an edge to the converter. */
+    cairo_status_t
+    (*add_edge)(
+	void		*abstract_converter,
+	cairo_fixed_t	 x1,
+	cairo_fixed_t	 y1,
+	cairo_fixed_t	 x2,
+	cairo_fixed_t	 y2);
+
+    /* Generates coverage spans for rows for the added edges and calls
+     * the renderer function for each row. After generating spans the
+     * only valid thing to do with the converter is to destroy it. */
+    cairo_status_t
+    (*generate)(
+	void			*abstract_converter,
+	cairo_span_renderer_t	*renderer);
+
+    /* Private status. Read with _cairo_scan_converter_status(). */
+    cairo_status_t status;
+};
+
+/* cairo-spans.c: */
+
+cairo_private cairo_scan_converter_t *
+_cairo_scan_converter_create_in_error (cairo_status_t error);
+
+cairo_private cairo_status_t
+_cairo_scan_converter_status (void *abstract_converter);
+
+cairo_private cairo_status_t
+_cairo_scan_converter_set_error (void *abstract_converter,
+				 cairo_status_t error);
+
+cairo_private cairo_span_renderer_t *
+_cairo_span_renderer_create_in_error (cairo_status_t error);
+
+cairo_private cairo_status_t
+_cairo_span_renderer_status (void *abstract_renderer);
+
+/* Set the renderer into an error state.  This sets all the method
+ * pointers except ->destroy() of the renderer to no-op
+ * implementations that just return the error status. */
+cairo_private cairo_status_t
+_cairo_span_renderer_set_error (void *abstract_renderer,
+				cairo_status_t error);
+
+#endif /* CAIRO_SPANS_PRIVATE_H */