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How do you draw a filled polygon in OpenGL?
By default OpenGL draws polygons in fill mode by filling in all the pixels enclosed within the boundary, but they can also be drawn in line mode as outlined polygons, or in point mode as points at the vertices. In OpenGL a polygon has a front and a back side.
What kind of polygon can OpenGL draw?
OpenGL supports several basic primitive types, including points, lines, quadrilaterals, and geneneral polygons. All of these primitives are specified using a sequence of vertices.
What kind of restrictions OpenGL imposes on primitive polygons Why?
The reason for the OpenGL restrictions on valid polygon types is that it’s simpler to provide fast polygon-rendering hardware for that restricted class of polygons. Simple polygons can be rendered quickly.
How does the OpenGL library break polygons into triangles?
OpenGL has many geometric primitives, but the fundamental drawing primitive is the triangle. The hardware in the GPU is designed to process triangles very efficiently. 1A [5 points]. OpenGL breaks all polygons (given by a sequence of n vertices inside of glBegin/glEnd) into triangles before drawing them.
What happens when an object to be drawn is not within the current viewport?
What happens when an object to be drawn is not within the current viewport? It is drawn by OpenGL even though it is not seen. A warning is given. It is clipped from the scene and subsequently not drawn.
How to force OpenGL to draw a non convex filled polygon?
During drawing, clear the stencil buffer along with the color buffer, and enable the stencil test. Set up state for the render pass that counts if pixels are rendered an odd/even number of times. Note that this must only write to the stencil buffer, so color writes are disabled.
Can you draw a triangle fan in OpenGL?
The main idea is that one can draw a triangle fan with an arbitrary origin and your polygon vertices. The pixels that are inside the polygon will then be drawn an odd number of times, while the pixels outside the polygons are drawn an even number of times. The stencil buffer is used to track the odd/even count.
How do you fill a line in OpenGL?
This algorithm works by intersecting scanline with polygon edges and fills the polygon between pairs of intersections. If both lines intersecting at the vertex are on the same side of the scanline, consider it as two points.
What is the purpose of scanline filling in OpenGL?
Scanline filling is basically filling up of polygons using horizontal lines or scanlines. The purpose of the SLPF algorithm is to fill (color) the interior pixels of a polygon given only the vertices of the figure.