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Exploring Special Visual Techniques: Blending, Fog, Antialiasing, and More in OpenGL

This chapter delves into advanced visual techniques in OpenGL, focusing on blending, atmospheric effects like fog, antialiasing practices, environment mapping, stencil buffer techniques, and bump mapping. Blending allows for more realistic graphics without overwriting pixel values, while fog enhances the atmosphere in scenes. Antialiasing ensures smoother visuals, and environment mapping simulates realistic reflections. The use of stencil buffers helps limit rendering areas, and bump mapping adds the perception of detail without altering geometry. Understanding these concepts is essential for creating immersive graphics.

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Exploring Special Visual Techniques: Blending, Fog, Antialiasing, and More in OpenGL

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  1. Chapter 13 Special Visual Techniques

  2. Blending • Without blending, a source fragment’s color values are supposed to overwrite those of its destination pixel. • With blending, the source fragment does not overwrite its destination pixel. • Pay attention to the z-value (depth testing). • Blending equation:

  3. Blending • Example: • source (0.6, 0.4, 0.2); dest (0.5, 0.5, 0.5) • SourceRb= SourceGb= SourceBb=0.3 • destRb= destGb= destBb=0.7 • Blending equation gives: • (0.3*0.5+0.7*0.6, 0.3*0.5+0.7*0.4, 0.3*0.5 +0.7*0.2) = (0.57, 0.43, 0.29)

  4. Blending

  5. Fog • Fog is an atmospheric effect that OpenGL offers ready to use. • glEnable(GL_FOG), glDisable(GL_FOG) • glFogfv(GL_FOG_COLOR, flgColor) • glFogi(GL_FOG_MODE, fogMode) • GL_LINEAR • GL_EXP • GL_EXP2

  6. Fog • GL_LINEAR: • GL_EXP: • GL_EXP2:

  7. Fog

  8. Antialiasing

  9. Antialiasing • Enable blending • Antialiasing itself is enabled with a call to • glEnable(GL_LINE_SMOOTH) • For the best possible antialiasing with the call • glHint(GL_LINE_SMOOTH_HINT, GL_NICEST)

  10. Environment Mapping • The goal of environment mapping is to simulate an object reflecting its surrounding, e.g., a shiny kettle reflecting the kitchen or a well-polished car reflecting the street. • Sphere Mapping • Cube Mapping

  11. Stencil Buffer Techniques • A stencil buffer is an extra buffer, in addition to the color buffer (pixel buffer) and depth buffer (z-buffering) found on modern graphics hardware. • Limit the area of rendering. • Make use of the strong connection between the depth buffer and the stencil buffer in the rendering pipeline. • Can put a heavy load on the graphics hardware.

  12. Bump Mapping • To give the illusion of geometric detail on a surface, e.g., making it appear ridged or dimpled, by means of perturbing the surface normals, but without actually changing any geometry.

  13. Raster Algorithms(Reading) • Cohen-Sutherland Line Clipper • Sutherland-Hodgeman Polygon Clipper • Bresenham line drawing • Polygon rasterizing

  14. Homework • Exercise 13.3

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