Set the value of a specific pixel in an image?

Setting the value of a pixel is a little more complex than reading it. on top of changing the pixel value with the "Fct_Pixel_Set_TAG()" method, you need to let the program know that you have changed a pixel. This is done through the "Fct_Update()" and "Fct_Redraw()" functions. Also, if you use the erase buffer, you need to update its status.

Here's an example of painting TAG values from the "Edit" mode.

#include "sliceO_include.hpp"

// ----------------------------------------------------------------------------

// Edit_Paint_Pix_Add()

// change the tag value under the brush

// Param: frame (SliceO_Frame *) ptr to the frame under the cursor

// pos_frm (Point_2D) cursor position in FRM space

// return: (void)

// ----------------------------------------------------------------------------

void Edit_Paint_Pix_Add( SliceO_Frame *frame, Point_2D *pos_frm )

{

short k, l ;

assert( frame ) ;

assert( frame->Fct_Pixel_Set_TAG ) ;

unsigned short TAG_Cur = (unsigned short) Fct_Variable_Value( "$TAG_CUR" ) ;

unsigned short *Brush_Size = (unsigned short *) Fct_Variable_Value( "$BRUSH_SIZE" ) ;

unsigned short Brush_Radius = (unsigned short) Fct_Variable_Value( "$BRUSH_RADIUS" ) ;

unsigned short Brush_Cur = (unsigned short) Fct_Variable_Value( "$BRUSH_CUR" ) ;

unsigned char ***Brush_Pt = (unsigned char ***) Fct_Variable_Value( "$BRUSH_PT" ) ;

// --- Get the brush's parameters ---

short b_size = Brush_Size[Brush_Cur] - 1 ;

short b_start = Brush_Radius - b_size ;

// --- compute brush position ---

Region_2D region( COORD_FRM,

(*pos_frm)[0] - b_size,

(*pos_frm)[1] - b_size,

(*pos_frm)[0] + b_size,

(*pos_frm)[1] + b_size ) ;

// --- stay inside the image ---

Region_2D cull( COORD_FRM, 0, 0, frame->m_x-1, frame->m_y-1 ) ;

short o_x=0 ;

if ( region[0] < 0.0f )

o_x = - (int) region[0] ;

short o_y=0 ;

if ( region[1] < 0.0f )

o_y = - (int) region[1] ;

if ( ! region.Cull( cull ) )

return ;

int modif = 0 ;

// --- change the actual tag values ---

Vect pos ;

pos.z = frame->m_z ;

pos.t = frame->m_t ;

for ( pos.y = region[1], l = b_start+o_y; pos.y <= region[3]; pos.y++, l++ )

for ( pos.x = region[0], k = b_start+o_x; pos.x <= region[2]; pos.x++, k++ )

if ( Brush_Pt[Brush_Cur][l][k] )

modif |= frame->Fct_Pixel_Set_TAG( frame, frame->m_ima, pos, (unsigned char) TAG_Cur ) ;

// --- if nothing change, get out ---

if ( ! modif )

return ;

// --- we updated the image, the erase buffer is now different from the image. ---

frame->Flag_Set_On( CLASS_MODE_THIS, CLASS_MODE_NONE, CLASS_FLAG_TAG_ERASE ) ;

Fct_Update( UPDATE_ERASE ) ;

// --- Update the displayed tag image ---

Fct_Update( UPDATE_DISPLAY_TAG, CLASS_MODE_ALL, frame, &region ) ;

// --- we will need a redraw of this portion of the screen ---

Fct_Redraw( REDRAW_DB_OPENGL, CLASS_MODE_ALL, frame, &region ) ;

}