Add support for offsets in ResampleEffect.

[movit] / resample_effect.cpp

diff --git a/resample_effect.cpp b/resample_effect.cpp
index 50b7c6bc5c4730fc6bb25cd18c96a446c8f02986..17745bc6d564e9340d756894b5f5058b34dbc1b8 100644 (file)
--- a/resample_effect.cpp
+++ b/resample_effect.cpp
@@ -171,6 +171,13 @@ bool ResampleEffect::set_float(const string &key, float value) {
                update_size();
                return true;
        }
+       if (key == "top") {
+               // Compensate for the bottom-left origin.
+               return vpass->set_float("offset", -value);
+       }
+       if (key == "left") {
+               return hpass->set_float("offset", value);
+       }
        return false;
 }
 
@@ -179,16 +186,19 @@ SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
          direction(HORIZONTAL),
          input_width(1280),
          input_height(720),
+         offset(0.0),
          last_input_width(-1),
          last_input_height(-1),
          last_output_width(-1),
-         last_output_height(-1)
+         last_output_height(-1),
+         last_offset(0.0 / 0.0)  // NaN.
 {
        register_int("direction", (int *)&direction);
        register_int("input_width", &input_width);
        register_int("input_height", &input_height);
        register_int("output_width", &output_width);
        register_int("output_height", &output_height);
+       register_float("offset", &offset);
 
        glGenTextures(1, &texnum);
 }
@@ -294,10 +304,12 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
        int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
        int src_samples = int_radius * 2 + 1;
        float *weights = new float[dst_samples * src_samples * 2];
+       float subpixel_offset = offset - lrintf(offset);  // The part not covered by whole_pixel_offset.
+       assert(subpixel_offset >= -0.5f && subpixel_offset <= 0.5f);
        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 + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
+               float center_src_y = (y + subpixel_offset + 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.
@@ -307,7 +319,6 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
                        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);
                }
-
        }
 
        // Now make use of the bilinear filtering in the GPU to reduce the number of samples
@@ -388,12 +399,14 @@ void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const strin
        if (input_width != last_input_width ||
            input_height != last_input_height ||
            output_width != last_output_width ||
-           output_height != last_output_height) {
+           output_height != last_output_height ||
+           offset != last_offset) {
                update_texture(glsl_program_num, prefix, sampler_num);
                last_input_width = input_width;
                last_input_height = input_height;
                last_output_width = output_width;
                last_output_height = output_height;
+               last_offset = offset;
        }
 
        glActiveTexture(GL_TEXTURE0 + *sampler_num);
@@ -411,6 +424,14 @@ void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const strin
        set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_bilinear_samples);
        set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_bilinear_samples);
 
+       float whole_pixel_offset;
+       if (direction == SingleResamplePassEffect::VERTICAL) {
+               whole_pixel_offset = lrintf(offset) / float(input_height);
+       } else {
+               whole_pixel_offset = lrintf(offset) / float(input_width);
+       }
+       set_uniform_float(glsl_program_num, prefix, "whole_pixel_offset", whole_pixel_offset);
+
        // We specifically do not want mipmaps on the input texture;
        // they break minification.
        Node *self = chain->find_node_for_effect(this);