pixel buffer vga in de2-115

hello, can anybody tell me how to send pixels to vga monitor. my code is:

alt_up_video_dma_dev* video;

for (i=0;i<rows,i++)

{

for (j=0;j<cols,j++)

{

color=(((img_R[i][j] >>8 ) & 0x0000F800)+ ((img_G[i][j] >>5 ) & 0x000007E0)(((img_B[i][j] >>3 ) & 0x0000001F));

alt_up_video_dma_draw(video,i,j,0);

}

}

the quality of the image displayed on the monitor is very bad, any clue?