Bugreport #4787 mentioned subpixel render issues, especially for small

images (like used for rendering icons).

When working during Orange on new render pipeline, I've left this topic
alone for a while... subpixel precision testing is very time consuming and
needs concentration for a while. :)

This commit brings back precision as it was for 2.41. Below a short
explanation of the solved issues.

- the window matrix for rendering is kept constant during all OSA passes,
  this to ensure clipping happens for each pass identically.
- a subpixel offset is only applied on filling in the z-buffer
- this offset is inverse corrected for shadepixel code, only on 2 places

Another nasty issue is that for filtered rendering (gauss etc), the tiles
(or entire image) is temporally increased 2 pixel in size. This caused a
'dark' (or sky color) edge on the rendering. During Orange that was solved
with a hardcoded clipping offset value, which only corrected for larger
pictures (like > 500 pixels in size).
Now this clipping offset is correctly calculated, based on render size.

Last issue: the view border in 3d window was calculated using integers,
giving small errors in display too. Now it uses float, so visually the
view border is more close to what a render shows.

8 files changed, 49 insertions, 40 deletions

diff --git a/source/blender/include/BSE_drawview.h b/source/blender/include/BSE_drawview.h
index 70793f88ce2..041381bbb1a 100644
--- a/source/blender/include/BSE_drawview.h
+++ b/source/blender/include/BSE_drawview.h
@@ -35,7 +35,7 @@
 
 struct Object;
 struct BGpic;
-struct rcti;
+struct rctf;
 struct ScrArea;
 struct ImBuf;
 
@@ -61,7 +61,7 @@ void drawview3dspace(struct ScrArea *sa, void *spacedata);
 void drawview3d_render(struct View3D *v3d, int winx, int winy);
 
 int update_time(void);
-void calc_viewborder(struct View3D *v3d, struct rcti *viewborder_r);
+void calc_viewborder(struct View3D *v3d, struct rctf *viewborder_r);
 void view3d_set_1_to_1_viewborder(struct View3D *v3d);
 
 int view3d_test_clipping(struct View3D *v3d, float *vec);
diff --git a/source/blender/render/intern/include/render_types.h b/source/blender/render/intern/include/render_types.h
index 8f0a85bd177..25ecf42b636 100644
--- a/source/blender/render/intern/include/render_types.h
+++ b/source/blender/render/intern/include/render_types.h
@@ -108,6 +108,7 @@ struct Render
 	rcti disprect;			/* part within winx winy */
 	rctf viewplane;			/* mapped on winx winy */
 	float viewdx, viewdy;	/* size of 1 pixel */
+	float clipcrop;			/* 2 pixel boundary to prevent clip when filter used */
 	
 	/* final picture width and height (within disprect) */
 	int rectx, recty;
@@ -120,7 +121,6 @@ struct Render
 	
 	/* values for viewing */
 	float lens, ycor, viewfac;
-	float bluroffsx, bluroffsy;
 	float panophi, panosi, panoco, panodxp, panodxv;
 	
 	/* Matrices */
diff --git a/source/blender/render/intern/source/initrender.c b/source/blender/render/intern/source/initrender.c
index 8b8a413762f..30beae1c467 100644
--- a/source/blender/render/intern/source/initrender.c
+++ b/source/blender/render/intern/source/initrender.c
@@ -456,8 +456,6 @@ void RE_SetCamera(Render *re, Object *camera)
 	rctf viewplane;
 	float pixsize, clipsta, clipend;
 	float lens;
-	float xd, yd;
-	int blursample= 0;	/* make new call for that */
 	
 	/* question mark */
 	re->ycor= ( (float)re->r.yasp)/( (float)re->r.xasp);
@@ -541,18 +539,12 @@ void RE_SetCamera(Render *re, Object *camera)
 			viewplane.ymax+= .5*re->ycor;
 		}
 	}
-
-	xd= yd= 0.0;
-	if(blursample != -1 && re->osa != 0 ) {
-		re->bluroffsx= xd= re->jit[blursample % re->osa][0];
-		re->bluroffsy= yd= re->ycor*re->jit[blursample % re->osa][1];
-	}
-	else re->bluroffsx=re->bluroffsy= 0.0f;
-
-	viewplane.xmin= pixsize*(viewplane.xmin+xd);
-	viewplane.xmax= pixsize*(viewplane.xmax+xd);
-	viewplane.ymin= pixsize*(viewplane.ymin+yd);
-	viewplane.ymax= pixsize*(viewplane.ymax+yd);
+	/* the window matrix is used for clipping, and not changed during OSA steps */
+	/* using an offset of +0.5 here would give clip errors on edges */
+	viewplane.xmin= pixsize*(viewplane.xmin);
+	viewplane.xmax= pixsize*(viewplane.xmax);
+	viewplane.ymin= pixsize*(viewplane.ymin);
+	viewplane.ymax= pixsize*(viewplane.ymax);
 	
 	re->viewdx= pixsize;
 	re->viewdy= re->ycor*pixsize;
@@ -562,7 +554,8 @@ void RE_SetCamera(Render *re, Object *camera)
 	else 
 		RE_SetWindow(re, &viewplane, clipsta, clipend);
 
-	//printmatrix4("win", re->winmat);
+	/* we clip faces with a minimum of 2 pixel boundary outside of image border. see zbuf.c */
+	re->clipcrop= 1.0f + 2.0f/(float)(re->winx>re->winy?re->winy:re->winx);
 }
 
 
diff --git a/source/blender/render/intern/source/rendercore.c b/source/blender/render/intern/source/rendercore.c
index c78ca424d91..2ae9ccc8527 100644
--- a/source/blender/render/intern/source/rendercore.c
+++ b/source/blender/render/intern/source/rendercore.c
@@ -2453,8 +2453,8 @@ void *shadepixel(ShadePixelInfo *shpi, float x, float y, int z, volatile int fac
 				float fx= 2.0/(R.winx*R.winmat[0][0]);
 				float fy= 2.0/(R.winy*R.winmat[1][1]);
 				
-				shi.co[0]= (0.5 + x - 0.5*R.winx)*fx - R.winmat[3][0]/R.winmat[0][0];
-				shi.co[1]= (0.5 + y - 0.5*R.winy)*fy - R.winmat[3][1]/R.winmat[1][1];
+				shi.co[0]= (x - 0.5*R.winx)*fx - R.winmat[3][0]/R.winmat[0][0];
+				shi.co[1]= (y - 0.5*R.winy)*fy - R.winmat[3][1]/R.winmat[1][1];
 				
 				/* using a*x + b*y + c*z = d equation, (a b c) is normal */
 				if(shi.facenor[2]!=0.0f)
@@ -2675,8 +2675,8 @@ void *shadepixel(ShadePixelInfo *shpi, float x, float y, int z, volatile int fac
 					float fx= 2.0/(R.rectx*R.winmat[0][0]);
 					float fy= 2.0/(R.recty*R.winmat[1][1]);
 					
-					shi.co[0]= (0.5 + x - 0.5*R.rectx)*fx - R.winmat[3][0]/R.winmat[0][0];
-					shi.co[1]= (0.5 + y - 0.5*R.recty)*fy - R.winmat[3][1]/R.winmat[1][1];
+					shi.co[0]= (x - 0.5*R.rectx)*fx - R.winmat[3][0]/R.winmat[0][0];
+					shi.co[1]= (y - 0.5*R.recty)*fy - R.winmat[3][1]/R.winmat[1][1];
 				}
 				
 				calc_view_vector(shi.view, x, y);
@@ -2697,6 +2697,10 @@ static void shadepixel_sky(ShadePixelInfo *shpi, float x, float y, int z, int fa
 	VlakRen *vlr;
 	float collector[4], rco[3];
 	
+	/* correction back for zbuffer filling in */
+	x+= 0.5f;
+	y+= 0.5f;
+	
 	vlr= shadepixel(shpi, x, y, z, facenr, mask, rco);
 	if(shpi->shr.combined[3] != 1.0) {
 		
diff --git a/source/blender/render/intern/source/zbuf.c b/source/blender/render/intern/source/zbuf.c
index 7cd21836469..3d685464574 100644
--- a/source/blender/render/intern/source/zbuf.c
+++ b/source/blender/render/intern/source/zbuf.c
@@ -1307,8 +1307,8 @@ static void clippyra(float *labda, float *v1, float *v2, int *b2, int *b3, int a
 		v13= v1[3];
 	}
 	else {
-		dw= 1.005f*(v2[3]-v1[3]);
-		v13= 1.005f*v1[3];
+		dw= R.clipcrop*(v2[3]-v1[3]);
+		v13= R.clipcrop*v1[3];
 	}	
 	/* according the original article by Liang&Barsky, for clipping of
 	 * homogenous coordinates with viewplane, the value of "0" is used instead of "-w" .
@@ -1527,7 +1527,6 @@ void zbufclip(ZSpan *zspan, int zvlnr, float *f1, float *f2, float *f3, int c1,
 	hoco_to_zco(zspan, vez, f1);
 	hoco_to_zco(zspan, vez+4, f2);
 	hoco_to_zco(zspan, vez+8, f3);
-
 	zspan->zbuffunc(zspan, zvlnr, vez,vez+4,vez+8, NULL);
 }
 
@@ -1628,6 +1627,7 @@ void zbuffer_solid(RenderPart *pa, unsigned int lay, short layflag)
 	/* needed for transform from hoco to zbuffer co */
 	zspan.zmulx=  ((float)R.winx)/2.0;
 	zspan.zmuly=  ((float)R.winy)/2.0;
+	
 	if(R.osa) {
 		zspan.zofsx= -pa->disprect.xmin - R.jit[pa->sample][0];
 		zspan.zofsy= -pa->disprect.ymin - R.jit[pa->sample][1];
@@ -1640,6 +1640,9 @@ void zbuffer_solid(RenderPart *pa, unsigned int lay, short layflag)
 		zspan.zofsx= -pa->disprect.xmin;
 		zspan.zofsy= -pa->disprect.ymin;
 	}
+	/* to centre the sample position */
+	zspan.zofsx -= 0.5f;
+	zspan.zofsy -= 0.5f;
 	
 	/* the buffers */
 	zspan.rectz= pa->rectz;
@@ -1752,8 +1755,8 @@ void RE_zbufferall_radio(struct RadView *vw, RNode **rg_elem, int rg_totelem, Re
 	zbuf_alloc_span(&zspan, vw->rectx, vw->recty);
 	zspan.zmulx=  ((float)vw->rectx)/2.0;
 	zspan.zmuly=  ((float)vw->recty)/2.0;
-	zspan.zofsx= 0;
-	zspan.zofsy= 0;
+	zspan.zofsx= -0.5f;
+	zspan.zofsy= -0.5f;
 	
 	/* the buffers */
 	zspan.rectz= vw->rectz;
@@ -2409,8 +2412,6 @@ static void zbuffer_abuf(RenderPart *pa, APixstr *APixbuf, ListBase *apsmbase, u
 	/* needed for transform from hoco to zbuffer co */
 	zspan.zmulx=  ((float)R.winx)/2.0;
 	zspan.zmuly=  ((float)R.winy)/2.0;
-	zspan.zofsx= -pa->disprect.xmin;
-	zspan.zofsy= -pa->disprect.ymin;
 	
 	/* the buffers */
 	zspan.arectz= MEM_mallocT(sizeof(int)*pa->rectx*pa->recty, "Arectz");
@@ -2430,13 +2431,20 @@ static void zbuffer_abuf(RenderPart *pa, APixstr *APixbuf, ListBase *apsmbase, u
 		zspan.mask= 1<<zsample;
 		
 		if(R.osa) {
-			zspan.zofsx= -pa->disprect.xmin-R.jit[zsample][0];
-			zspan.zofsy= -pa->disprect.ymin-R.jit[zsample][1];
+			zspan.zofsx= -pa->disprect.xmin - R.jit[zsample][0];
+			zspan.zofsy= -pa->disprect.ymin - R.jit[zsample][1];
 		}
 		else if(R.i.curblur) {
 			zspan.zofsx= -pa->disprect.xmin - R.jit[R.i.curblur-1][0];
 			zspan.zofsy= -pa->disprect.ymin - R.jit[R.i.curblur-1][1];
 		}
+		else {
+			zspan.zofsx= -pa->disprect.xmin;
+			zspan.zofsy= -pa->disprect.ymin;
+		}
+		/* to centre the sample position */
+		zspan.zofsx -= 0.5f;
+		zspan.zofsy -= 0.5f;
 		
 		for(v=0; v<R.totvlak; v++) {
 			if((v & 255)==0)
@@ -2605,6 +2613,10 @@ static void shadetrapixel(ShadePixelInfo *shpi, float x, float y, int z, int fac
 		printf("error in shadetrapixel nr: %d\n", (facenr & RE_QUAD_MASK));
 		return;
 	}
+	/* correction back for zbuffer filling in */
+	x+= 0.5f;
+	y+= 0.5f;
+	
 	if(R.osa) {
 		VlakRen *vlr= RE_findOrAddVlak(&R, (facenr-1) & RE_QUAD_MASK);
 		float accumcol[4]={0,0,0,0}, tot=0.0;
diff --git a/source/blender/src/drawview.c b/source/blender/src/drawview.c
index e7d9bfdbbd1..dc7b0d0f2d0 100644
--- a/source/blender/src/drawview.c
+++ b/source/blender/src/drawview.c
@@ -393,7 +393,7 @@ static void draw_bgpic(void)
 	}
 
 	if(G.vd->persp==2) {
-		rcti vb;
+		rctf vb;
 
 		calc_viewborder(G.vd, &vb);
 
@@ -864,7 +864,7 @@ static void view3d_get_viewborder_size(View3D *v3d, float size_r[2])
 	}
 }
 
-void calc_viewborder(struct View3D *v3d, rcti *viewborder_r)
+void calc_viewborder(struct View3D *v3d, rctf *viewborder_r)
 {
 	float zoomfac, size[2];
 	float dx= 0.0f, dy= 0.0f;
@@ -964,7 +964,7 @@ static void drawviewborder(void)
 	float fac, a;
 	float x1, x2, y1, y2;
 	float x3, y3, x4, y4;
-	rcti viewborder;
+	rctf viewborder;
 	Camera *ca= NULL;
 
 	if(G.vd->camera==NULL)
diff --git a/source/blender/src/edit.c b/source/blender/src/edit.c
index c48539ba736..bad89da633f 100644
--- a/source/blender/src/edit.c
+++ b/source/blender/src/edit.c
@@ -247,7 +247,7 @@ int get_border(rcti *rect, short flag)
 						BMF_DrawString(G.fonts, str);
 					}
 					else if(G.vd->persp==2) {
-						rcti vb;
+						rctf vb;
 	
 						calc_viewborder(G.vd, &vb);
 	
diff --git a/source/blender/src/editview.c b/source/blender/src/editview.c
index 76d857826b6..001105c43a9 100644
--- a/source/blender/src/editview.c
+++ b/source/blender/src/editview.c
@@ -1980,14 +1980,14 @@ void set_render_border(void)
 	
 	val= get_border(&rect, 3);
 	if(val) {
-		rcti vb;
+		rctf vb;
 
 		calc_viewborder(G.vd, &vb);
 
-		G.scene->r.border.xmin= (float) (rect.xmin-vb.xmin)/(vb.xmax-vb.xmin);
-		G.scene->r.border.ymin= (float) (rect.ymin-vb.ymin)/(vb.ymax-vb.ymin);
-		G.scene->r.border.xmax= (float) (rect.xmax-vb.xmin)/(vb.xmax-vb.xmin);
-		G.scene->r.border.ymax= (float) (rect.ymax-vb.ymin)/(vb.ymax-vb.ymin);
+		G.scene->r.border.xmin= ((float)rect.xmin-vb.xmin)/(vb.xmax-vb.xmin);
+		G.scene->r.border.ymin= ((float)rect.ymin-vb.ymin)/(vb.ymax-vb.ymin);
+		G.scene->r.border.xmax= ((float)rect.xmax-vb.xmin)/(vb.xmax-vb.xmin);
+		G.scene->r.border.ymax= ((float)rect.ymax-vb.ymin)/(vb.ymax-vb.ymin);
 		
 		CLAMP(G.scene->r.border.xmin, 0.0, 1.0);
 		CLAMP(G.scene->r.border.ymin, 0.0, 1.0);