eeshow/gfx/: don't overthink coordinate transforms

The xe/ye element was completely unnecessary because we never have an
offset at the pixel level. Furthermore, it was used incorrectly, causing
a shift between old and new when xmin/ymin differed.

eeshow/gfx/cro.c

@@ -45,7 +45,6 @@ struct cro_ctx {
 	struct record record;	/* must be first */
 
 	int xo, yo;		/* offset in target (e.g., canvas) coord */
-	int xe, ye;		/* additional offset in eeschema coord */
 	float scale;
 
 	cairo_t *cr;
@@ -74,13 +73,13 @@ static inline int dc(const struct cro_ctx *cc, int x)
 
 static inline int cx(const struct cro_ctx *cc, int x)
 {
-	return cc->xo + (x + cc->xe) * cc->scale;
+	return cc->xo + x * cc->scale;
 }
 
 
 static inline int cy(const struct cro_ctx *cc, int y)
 {
-	return cc->yo + (y + cc->ye) * cc->scale;
+	return cc->yo + y * cc->scale;
 }
 
 
@@ -265,7 +264,6 @@ static struct cro_ctx *new_cc(void)
 
 	cc = alloc_type(struct cro_ctx);
 	cc->xo = cc->yo = 0;
-	cc->xe = cc->ye = 0;
 	cc->scale = DEFAULT_SCALE;
 
 	cc->sheets = NULL;
@@ -535,7 +533,6 @@ void cro_canvas_draw(struct cro_ctx *cc, cairo_t *cr, int xo, int yo,
 
 
 uint32_t *cro_img(struct cro_ctx *ctx, int xo, int yo, int w, int h,
-    int xe, int ye,
     float scale, cairo_t **res_cr, int *res_stride)
 {
 	int stride;
@@ -562,8 +559,6 @@ uint32_t *cro_img(struct cro_ctx *ctx, int xo, int yo, int w, int h,
 	ctx->s = s;
 	ctx->xo = xo;
 	ctx->yo = yo;
-	ctx->xe = xe;
-	ctx->ye = ye;
 	ctx->scale = scale;
 	ctx->color_override = COLOR_NONE;
 

eeshow/gfx/cro.h

@@ -44,7 +44,6 @@ void cro_canvas_draw(struct cro_ctx *cc, cairo_t *cr,
     int x, int y, float scale);
 
 uint32_t *cro_img(struct cro_ctx *ctx, int x0, int yo, int w, int h,
-    int xe, int ye,
     float scale, cairo_t **res_cr, int *res_stride);
 
 #endif /* !GFX_CRO_H */

eeshow/gfx/diff.c

@@ -350,29 +350,15 @@ void diff_to_canvas(cairo_t *cr, int cx, int cy, float scale,
 	merge_coord(old_xmin, new_xmin, old_w, new_w, &xmin, &w);
 	merge_coord(old_ymin, new_ymin, old_h, new_h, &ymin, &h);
 
-	/*
-	 * We use two sets of offset differences: one applied to eeschema
-	 * coordinates (the xe, ye pair), and one applied to canvas coordinates
-	 * (the xo, yo pair).
-	 *
-	 * This is to prevent different offsets from leading to rounding
-	 * differences, resulting in single-pixel differences, which in turn
-	 * the differences algorithm will be eager to mark with big yellow
-	 * boxes.
-	 */
 	img_old = cro_img(old,
 	    sw / 2.0 - (cx + xmin) * scale,
 	    sh / 2.0 - (cy + ymin) * scale,
 	    sw, sh,
-	    xmin - old_xmin,
-	    ymin - old_ymin,
 	    scale, &old_cr, &stride);
 	img_new = cro_img(new,
 	    sw / 2.0 - (cx + xmin) * scale,
 	    sh / 2.0 - (cy + ymin) * scale,
 	    sw, sh,
-	    xmin - new_xmin,
-	    ymin - new_ymin,
 	    scale, NULL, NULL);
 
 	struct diff diff = {