gfx_blitext(source, coordinatelist, rotation) -- REAPER 2.018+
This is a version of gfx_blit which takes many of its parameters via a buffer rather than direct parameters.
For the "source" parameter specify -1 to use the main framebuffer as source, or 0..127 to use the image specified (or PNG file in a filename: line).
coordinatelist should be an index to memory where a list of 10 parameters are stored, such as:
coordinatelist=1000; // use memory slots 1000-1009
coordinatelist[0]=source_x;
coordinatelist[1]=source_y;
coordinatelist[2]=source_w;
coordinatelist[3]=source_h;
coordinatelist[4]=dest_x;
coordinatelist[5]=dest_y;
coordinatelist[6]=dest_w;
coordinatelist[7]=dest_h;
coordinatelist[8]=rotation_x_offset; // only used if rotation is set, represents offset from center of image
coordinatelist[9]=rotation_y_offset; // only used if rotation is set, represents offset from center of image
gfx_blitext(img,coordinatelist,angle);