blending /depth_test

[nv_dv]

trying to render multiple aplha maps ONE_MINUS_SRC.... but
blending seems to only works with object rendered from back to top

eg: A is rendered before B , but B is lower (on depth_test)



/////////////////////////////// Render tree (stock) /////////////////////////////////

vtx_smap(){
	extern m_cnt,m_start;
	extern f_cnt,f_start;

	struct vtx_flg *rend;
	struct vtx_map *midx;
	struct vtx *vec;

	uint x,i,j;

	rend= f_start; 
	midx= m_start; 
	vec= v_start;

	//----------------------------------------- LAYER
	for( x=0; x < activl ; x++){


		////// texture
		if( rend->flg&VL_TEX){
			activtex( rend->rsd, rend->tex);
			glEnable( GL_TEXTURE_2D);	
		}

			///////////////////////////////
			if( rend->flg&VL_RS)	glDepthMask( GL_FALSE);
			//////////////////////////////

		////////// blend	
		if( rend->flg&VL_MASK ){
		glEnable( GL_BLEND);
			/* high_light  */
			if( rend->flg&VL_LONL) glBlendFunc( GL_SRC_ALPHA, GL_ONE);
			/* alpha channel */
			if( rend->flg&VL_AC) glBlendFunc( GL_SRC_ALPHA , GL_ONE_MINUS_SRC_ALPHA); 
			/* overlay  */
			if( rend->flg&VL_OL) glBlendFunc( GL_DST_COLOR, GL_DST_COLOR); 
			
		}


	glBegin( GL_TRIANGLE_STRIP);

		for( i= 0; i < rend->idxL; i++){ //IDXL


 			for( j= 1; j < midx->idx ;j++)
			if( j < v_cnt)
			vec= vec->next;
		

			if( rend->flg&VL_SUV)
				glTexCoord2f( midx->s, midx->t);
		
			else
				glTexCoord2f( vec->s, vec->t);
		
			
			if( rend->flg&VL_SRGB)
				glColor4ub( midx->r, midx->g, midx->b, midx->a);
	
			else
				glColor4ub( vec->r, vec->g, vec->b, vec->a);
		

			glVertex3f( vec->x, vec->y, vec->z);


		vec= v_start;
		midx= midx->next;

		}//--------------------------- IDXL


	glEnd();

	////////////////////////////
	if( rend->flg&VL_TEX) glDisable( GL_TEXTURE_2D);
	///////////////////////////////
	if( rend->flg&VL_RS)	glDepthMask( GL_TRUE);
	//////////////////////////////
	if( rend->flg&VL_MASK) glDisable( GL_BLEND);
	

	rend= rend->next;
	}//f_cnt -----------------------LAYER
}

init()
----------------------------------------------------------------------------
glClearColor( r, g, b, a); //default bg
//default matrix is on modelview


//glMatrixMode( GL_MODELVIEW); //default
//glLoadIdentity();


glPerspecv( view); //NEHE
set_vpos( v_pos); //set cam

glCullFace( GL_BACK);
glPointSize( 1.5);
glEnable( GL_CULL_FACE);
--------------------------------------------------------------------------------

render()
--------------------------------------------------------------------------------------------
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );


extern float v_pos[3]; //view pos (z)



glPushMatrix();
////////////////////// view dist
set_vpos( v_pos);
////////////////////////////////

glRotatef( rt[0], 1.0,.0,.0);
glRotatef( rt[1], .0,1.0,.0);
glTranslatef( wt[0], wt[1], wt[2]);

glPushMatrix();

///////////////////////////////////////////////////////
glEnable( GL_DEPTH_TEST);


vtx_smap(); //<---------------------- render tree + enable/disable Blend


glDisable( GL_DEPTH_TEST);
///////////////////////////////////////////////////////

glPopMatrix();

glPopMatrix();

vtx_menu( -0.55,0.12,1,28);

cursor( tool);

=================================================

is there any way you can correctly blend surfaces regardless of rendering order

 

[3dcgi]

Look for a method titled order independent transparency with linked lists. AMD published details about a method and Intel has as well.

 

[nv_dv]

Thanks, good thing i wont have to worry about the other platform :smile:

 

[Davros]

That reply makes it sound like you think the above solutions will not work on nv hardware

 

[MrGaribaldi]

As 3dcgi says, both AMD and intel have papers on this, with slightly different approaches.
Here is a nice presentation, with informative pictures, of AMDs solution. And here you can find Intels GDC presentation and source code.


But I recommend that you look at what Cyril Crassin has done, since he too is using OpenGL. You should be able to re-implement it with standard OpenGL, and if you want to save space you can use intels AT approach with it.

 

[nv_dv]

That reply makes it sound like you think the above solutions will not work on nv hardware

not at all , i was reffering the other platform as an old embded system using a PVR gpu
apparently there's automatic OIT support in hardware

@MrGaribaldi
thanks

 

[Rodéric]

not at all , i was reffering the other platform as an old embded system using a PVR gpu
apparently there's automatic OIT support in hardware

@MrGaribaldi
thanks

That would be a Dreamcast or a Naomi arcade board, as they are the only ones featuring that capability. (AFAIK)

 

[Dominik D]

OIT is supported on SGX as long as depth writes are disabled. (AFAIK)

 

[frogblast]

OIT is supported on SGX as long as depth writes are disabled. (AFAIK)

Nope. I think Imagination stopped doing OIT way back sometime in the dreamcast timeframe.

Current Imagination devices will always blend strictly in submission order, just like every other GPU (and like OGL/D3D mandate).