frame transformer for wasm

frame-transformer.c

#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

#define WASM_EXPORT __attribute__((visibility("default")))

uint16_t w;   // frame width
uint16_t h ;  // frame height
uint8_t * input_buffer;
uint8_t * out_buffer;
uint8_t * bg_buffer ;  // buffer for background image 

WASM_EXPORT
uint8_t * init_in(uint16_t w_in, uint16_t h_in) {
  w = w_in;
  h = h_in;
  input_buffer = malloc(w*h*1.5) ;      // input buffer for YUV format
  return input_buffer ;
}

WASM_EXPORT
uint8_t * init_out(void) {
  out_buffer = malloc(w*h*4) ;   // output buffer for RGBA format
  return out_buffer ;
}

WASM_EXPORT
uint8_t * init_bg_img(void) {
  bg_buffer = malloc(w*h*4) ;   // background image, RGBA format
  return bg_buffer ;
}

// saturation function
inline uint8_t sat (float val) {
  if (val > 255) return 255;
  if (val < 0) return 0;
  return (uint8_t)val ;
};

// frame processor function
WASM_EXPORT
void process(uint32_t stride, uint32_t offset1, uint32_t offset2) {
  uint32_t xUV = 0;
  uint32_t yUV = 0;
      for (uint32_t y=0; y != h; y++) {
        yUV = (y >> 1) * stride;
        for (uint32_t x= 0; x != w; x++) {
          xUV = x >> 1;
          float Y = (float)input_buffer[x + y * w];
          float V = (float)input_buffer[offset1 + xUV + yUV] - 128;
          float U = (float)input_buffer[offset2 + xUV + yUV] - 128;

          uint8_t R = sat(Y + 1.370705 * V);
          uint8_t G = sat(Y - 0.698001 * V - 0.337633 * U);
          uint8_t B = sat(Y + 1.732446 * U);

          uint32_t p = x * 4 + y * w * 4 ;
          if ( G > 0.6 * (R + B) ) {
            R = bg_buffer[0 + p];
            G = bg_buffer[1 + p];
            B = bg_buffer[2 + p];
          }

          out_buffer[0 + p] = R;
          out_buffer[1 + p] = G;
          out_buffer[2 + p] = B;
          out_buffer[3 + p] = 255;
        }
      }
}