136 lines
3.6 KiB
C
136 lines
3.6 KiB
C
/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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*/
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#include "config.h"
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#include <cairo/cairo.h>
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#include <stdint.h>
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#include <string.h>
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/*
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* Arbitrary hash function whhich maps ALL 32-bit numbers onto 24-bit numbers
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* evenly, while guaranteeing that all 24-bit numbers are mapped onto
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* themselves.
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*/
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unsigned int _guac_hash_32to24(unsigned int value) {
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/* Grab highest-order byte */
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unsigned int upper = value & 0xFF000000;
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/* XOR upper with lower three bytes, truncate to 24-bit */
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return
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(value & 0xFFFFFF)
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^ (upper >> 8)
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^ (upper >> 16)
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^ (upper >> 24);
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}
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/**
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* Rotates a given 32-bit integer by N bits.
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*
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* NOTE: We probably should check for available bitops.h macros first.
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*/
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unsigned int _guac_rotate(unsigned int value, int amount) {
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/* amount = amount % 32 */
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amount &= 0x1F;
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/* Return rotated amount */
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return (value >> amount) | (value << (32 - amount));
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}
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unsigned int guac_hash_surface(cairo_surface_t* surface) {
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/* Init to zero */
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unsigned int hash_value = 0;
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int x, y;
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/* Get image data and metrics */
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unsigned char* data = cairo_image_surface_get_data(surface);
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int width = cairo_image_surface_get_width(surface);
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int height = cairo_image_surface_get_height(surface);
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int stride = cairo_image_surface_get_stride(surface);
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for (y=0; y<height; y++) {
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/* Get current row */
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uint32_t* row = (uint32_t*) data;
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data += stride;
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for (x=0; x<width; x++) {
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/* Get color at current pixel */
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unsigned int color = *row;
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row++;
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/* Compute next hash */
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hash_value =
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_guac_rotate(hash_value, 1) ^ color ^ 0x1B872E69;
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}
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} /* end for each row */
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/* Done */
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return _guac_hash_32to24(hash_value);
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}
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int guac_surface_cmp(cairo_surface_t* a, cairo_surface_t* b) {
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/* Surface A metrics */
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unsigned char* data_a = cairo_image_surface_get_data(a);
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int width_a = cairo_image_surface_get_width(a);
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int height_a = cairo_image_surface_get_height(a);
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int stride_a = cairo_image_surface_get_stride(a);
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/* Surface B metrics */
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unsigned char* data_b = cairo_image_surface_get_data(b);
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int width_b = cairo_image_surface_get_width(b);
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int height_b = cairo_image_surface_get_height(b);
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int stride_b = cairo_image_surface_get_stride(b);
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int y;
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/* If core dimensions differ, just compare those. Done. */
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if (width_a != width_b) return width_a - width_b;
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if (height_a != height_b) return height_a - height_b;
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for (y=0; y<height_a; y++) {
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/* Compare row. If different, use that result. */
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int cmp_result = memcmp(data_a, data_b, width_a * 4);
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if (cmp_result != 0)
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return cmp_result;
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/* Next row */
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data_a += stride_a;
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data_b += stride_b;
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}
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/* Otherwise, same. */
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return 0;
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}
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