150 lines
4.3 KiB
C
150 lines
4.3 KiB
C
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#include "imagescaler.h"
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#include <cstdlib>
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#include <cmath>
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ImageScaler::ImageScaler() :
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m_memory(NULL),
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m_hor_filters(NULL),
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m_ver_filters(NULL),
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m_buffer(NULL),
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m_dst_image(NULL),
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m_dst_stride(0),
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m_dst_width(0),
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m_dst_height(0),
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m_src_width(0),
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m_src_height(0),
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m_src_x(0),
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m_src_y(0),
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m_dst_x(0),
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m_dst_y(0) {
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}
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ImageScaler::~ImageScaler() {
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if ( m_memory ) free( m_memory );
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}
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// sin(x)/(x)
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static float sincf( float x ) {
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if ( fabsf(x) < 0.05f ) return 1.0f - (1.0f/6.0f)*x*x; // taylor series approximation to avoid 0/0
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return sin(x)/x;
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}
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static void CalculateFilters( ImageScaler::Filter *filters, int dst_size, int src_size ) {
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const float fc = dst_size >= src_size ? 1.0f : ((float) dst_size)/((float) src_size);
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for (int i = 0; i < dst_size; i++) {
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const int d = 2*dst_size; // sample position denominator
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const int e = (2*i+1) * src_size - dst_size; // sample position enumerator
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int offset = e / d; // truncated sample position
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const float sub_offset = ((float) (e - offset*d)) / ((float) d); // exact sample position is (float) e/d = offset + sub_offset
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// calculate filter coefficients
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float h[4];
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for (int j=0; j<4; j++) {
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const float t = 3.14159265359f * (sub_offset+(1-j));
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h[j] = sincf( fc * t ) * cosf( 0.25f * t ); // sinc-lowpass and cos-window
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}
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// ensure that filter does not reach out off image bounds:
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while ( offset < 1 ) {
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h[0] += h[1];
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h[1] = h[2];
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h[2] = h[3];
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h[3] = 0.0f;
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offset++;
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}
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while ( offset+3 > src_size ) {
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h[3] += h[2];
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h[2] = h[1];
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h[1] = h[0];
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h[0] = 0.0f;
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offset--;
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}
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// coefficients are normalized to sum up to 2048
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const float norm = 2048.0f / ( h[0] + h[1] + h[2] + h[3] );
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offset--; // offset of fist used pixel
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filters[i].m_offset = offset + 4; // store offset of first unused pixel
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for (int j=0; j<4; j++) {
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const float t = norm * h[j];
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filters[i].m_coeff[(offset+j) & 3] = (int) ((t > 0.0f) ? (t+0.5f) : (t-0.5f)); // consider ring buffer index permutations
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}
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}
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// set end marker
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filters[dst_size].m_offset = (unsigned) -1;
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}
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void ImageScaler::SetImageParameters( unsigned *dst_image, unsigned dst_stride, unsigned dst_width, unsigned dst_height, unsigned src_width, unsigned src_height ) {
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m_src_x = 0;
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m_src_y = 0;
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m_dst_x = 0;
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m_dst_y = 0;
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m_dst_image = dst_image;
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m_dst_stride = dst_stride;
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// if image dimensions do not change we can keep the old filter coefficients
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if ( (src_width == m_src_width) && (src_height == m_src_height) && (dst_width == m_dst_width) && (dst_height == m_dst_height) ) return;
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m_dst_width = dst_width;
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m_dst_height = dst_height;
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m_src_width = src_width;
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m_src_height = src_height;
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if ( m_memory ) free( m_memory );
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const unsigned hor_filters_size = (m_dst_width + 1) * sizeof(Filter); // reserve one extra position for end marker
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const unsigned ver_filters_size = (m_dst_height + 1) * sizeof(Filter);
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const unsigned buffer_size = 4 * m_dst_width * sizeof(TmpPixel);
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char *p = (char *) malloc( hor_filters_size + ver_filters_size + buffer_size );
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m_memory = p;
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m_hor_filters = (Filter *) p; p += hor_filters_size;
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m_ver_filters = (Filter *) p; p += ver_filters_size;
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m_buffer = (TmpPixel *) p;
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CalculateFilters( m_hor_filters, m_dst_width , m_src_width );
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CalculateFilters( m_ver_filters, m_dst_height, m_src_height );
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}
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// shift range to 0..255 and clamp overflows
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static unsigned shift_clamp( int x ) {
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x = ( x + (1<<21) ) >> 22;
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if ( x < 0 ) return 0;
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if ( x > 255 ) return 255;
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return x;
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}
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void ImageScaler::NextSourceLine() {
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m_dst_x = 0;
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m_src_x = 0;
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m_src_y++;
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while ( m_ver_filters[m_dst_y].m_offset == m_src_y ) {
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const int h0 = m_ver_filters[m_dst_y].m_coeff[0];
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const int h1 = m_ver_filters[m_dst_y].m_coeff[1];
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const int h2 = m_ver_filters[m_dst_y].m_coeff[2];
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const int h3 = m_ver_filters[m_dst_y].m_coeff[3];
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const TmpPixel *src = m_buffer;
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unsigned *dst = m_dst_image + m_dst_stride * m_dst_y;
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for (unsigned i=0; i<m_dst_width; i++) {
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const ImageScaler::TmpPixel t( src[0]*h0 + src[1]*h1 + src[2]*h2 + src[3]*h3 );
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src += 4;
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dst[i] = shift_clamp(t[0]) | (shift_clamp(t[1])<<8) | (shift_clamp(t[2])<<16) | (shift_clamp(t[3])<<24);
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}
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m_dst_y++;
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}
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}
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