UI: Fix draw issues with multiview projector

Scissor rects would affect the internal effect rendering of sources, so
scissor rectangles aren't the ideal method of restricting draw space.
Instead, use viewports and projection matrices, which are automatically
accounted for by internal source handling.

UI/window-projector.cpp

@@ -250,7 +250,6 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 		     hiCX, hiCY, qiX, qiY, qiCX, qiCY,
 		     hiScaleX, hiScaleY, qiScaleX, qiScaleY;
 	uint32_t     offset;
-	gs_rect      rect;
 
 	gs_effect_t  *solid = obs_get_base_effect(OBS_EFFECT_SOLID);
 	gs_eparam_t  *color = gs_effect_get_param_by_name(solid, "color");
@@ -294,6 +293,30 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 			gs_draw_sprite(nullptr, 0, (uint32_t)cx, (uint32_t)cy);
 	};
 
+	auto setRegion = [fX, fY, scale] (float x, float y, float cx, float cy)
+	{
+		float vX  = int(fX + x * scale);
+		float vY  = int(fY + y * scale);
+		float vCX = int(cx * scale);
+		float vCY = int(cy * scale);
+
+		float oL = x;
+		float oT = y;
+		float oR = (x + cx);
+		float oB = (y + cy);
+
+		gs_projection_push();
+		gs_viewport_push();
+		gs_set_viewport(vX, vY, vCX, vCY);
+		gs_ortho(oL, oR, oT, oB, -100.0f, 100.0f);
+	};
+
+	auto resetRegion = [] ()
+	{
+		gs_viewport_pop();
+		gs_projection_pop();
+	};
+
 	/* ----------------------------- */
 	/* draw sources                  */
 
@@ -322,11 +345,6 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 		qiX = sourceX + 4.0f;
 		qiY = sourceY + 4.0f;
 
-		rect.x = int(fX + qiX * scale);
-		rect.y = int(fY + qiY * scale);
-		rect.cx = int(qiCX * scale);
-		rect.cy = int(qiCY * scale);
-
 		/* ----------- */
 
 		if (src == previewSrc || src == programSrc) {
@@ -351,10 +369,10 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 		gs_matrix_translate3f(qiX, qiY, 0.0f);
 		gs_matrix_scale3f(qiScaleX, qiScaleY, 1.0f);
 
-		gs_effect_set_color(color, 0xFF000000);
-		gs_set_scissor_rect(&rect);
+		setRegion(qiX, qiY, qiCX, qiCY);
 		obs_source_video_render(src);
-		gs_set_scissor_rect(nullptr);
+		resetRegion();
+
 		gs_effect_set_color(color, 0xFFFFFFFF);
 		renderVB(solid, window->outerBox, targetCX, targetCY);
 
@@ -362,7 +380,6 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 
 		/* ----------- */
 
-
 		offset = labelOffset(label, quarterCX);
 		cx = obs_source_get_width(label);
 		cy = obs_source_get_height(label);
@@ -386,11 +403,7 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 	gs_matrix_translate3f(2.0f, 2.0f, 0.0f);
 	gs_matrix_scale3f(hiScaleX, hiScaleY, 1.0f);
 
-	rect.x = int(fX + 2.0f * scale);
-	rect.y = int(fY + 2.0f * scale);
-	rect.cx = int(hiCX * scale);
-	rect.cy = int(hiCY * scale);
-	gs_set_scissor_rect(&rect);
+	setRegion(2.0f, 2.0f, hiCX, hiCY);
 
 	if (studioMode) {
 		obs_source_video_render(previewSrc);
@@ -398,7 +411,7 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 		obs_render_main_view();
 	}
 
-	gs_set_scissor_rect(nullptr);
+	resetRegion();
 
 	gs_matrix_pop();
 
@@ -439,13 +452,9 @@ void OBSProjector::OBSRenderMultiview(void *data, uint32_t cx, uint32_t cy)
 	gs_matrix_translate3f(halfCX + 2.0, 2.0f, 0.0f);
 	gs_matrix_scale3f(hiScaleX, hiScaleY, 1.0f);
 
-	rect.x = int(fX + (halfCX + 2.0f) * scale);
-	rect.y = int(fY + 2.0f * scale);
-	gs_set_scissor_rect(&rect);
-
+	setRegion(halfCX + 2.0f, 2.0f, hiCX, hiCY);
 	obs_render_main_view();
-
-	gs_set_scissor_rect(nullptr);
+	resetRegion();
 
 	gs_matrix_pop();