for (unsigned y = 0; y < dst_samples; ++y) {
// Find the point around which we want to sample the source image,
// compensating for differing pixel centers as the scale changes.
- float center_src_y = (y + subpixel_offset + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
+ float center_src_y = (y + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
int base_src_y = lrintf(center_src_y);
// Now sample <int_radius> pixels on each side around that point.
for (int i = 0; i < src_samples; ++i) {
int src_y = base_src_y + i - int_radius;
- float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y), LANCZOS_RADIUS);
+ float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y - subpixel_offset), LANCZOS_RADIUS);
weights[(y * src_samples + i) * 2 + 0] = weight * radius_scaling_factor;
weights[(y * src_samples + i) * 2 + 1] = (src_y + 0.5) / float(src_size);
}
expect_equal(expected_data, out_data, width, height);
}
+TEST(ResampleEffectTest, ReadHalfPixelFromLeftAndScale) {
+ const int src_width = 4;
+ const int dst_width = 8;
+
+ float data[src_width * 1] = {
+ 1.0, 2.0, 3.0, 4.0,
+ };
+ float expected_data[dst_width * 1] = {
+ // Empirical; the real test is that we are the same for 0.499 and 0.501.
+ 1.1553, 1.7158, 2.2500, 2.7461, 3.2812, 3.8418, 4.0703, 4.0508
+ };
+ float out_data[dst_width * 1];
+
+ EffectChainTester tester(NULL, dst_width, 1, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR);
+
+ ImageFormat format;
+ format.color_space = COLORSPACE_sRGB;
+ format.gamma_curve = GAMMA_LINEAR;
+
+ FlatInput *input = new FlatInput(format, FORMAT_GRAYSCALE, GL_FLOAT, src_width, 1);
+ input->set_pixel_data(data);
+ tester.get_chain()->add_input(input);
+
+ Effect *resample_effect = tester.get_chain()->add_effect(new ResampleEffect());
+ ASSERT_TRUE(resample_effect->set_int("width", dst_width));
+ ASSERT_TRUE(resample_effect->set_int("height", 1));
+
+ // Check that we are (almost) the same no matter the rounding.
+ ASSERT_TRUE(resample_effect->set_float("left", 0.499f));
+ tester.run(out_data, GL_RED, COLORSPACE_sRGB, GAMMA_LINEAR);
+ expect_equal(expected_data, out_data, dst_width, 1);
+
+ ASSERT_TRUE(resample_effect->set_float("left", 0.501f));
+ tester.run(out_data, GL_RED, COLORSPACE_sRGB, GAMMA_LINEAR);
+ expect_equal(expected_data, out_data, dst_width, 1);
+}
+
} // namespace movit