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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Rendering techniques generally involve setting a color or color function across each component, often based on the effects of a light source from the observer to the screen. For example, a square polygon facing the observer may be red, while its color may change toward darker shades of red as the polygon is rotated, becoming completely dark when 90° from the observer. Shading techniques may compute color as a continuous function across a component. Gouraud shading, for example, interpolates a color value across a polygon from its corner values, while another technique known as Phong shading computes color from an interpolation of the light source vector itself across the polygon. More advanced rendering techniques include ray tracing, which computes the behavior of light rays to simulate effects such as reflectance, shadows, and translucency, and texture mapping, which simulates a pattern or image across surfaces of the displayed model.
Hiding Media Data via Shaders: Enabling Private Sharing in the Clouds
Published in Kaikai Liu, Xiaolin Li, Mobile SmartLife via Sensing, Localization, and Cloud Ecosystems, 2017
Fig. 11.3 shows our designed secure media sharing process to open social media channels. We leverage the image key in addition to the normal key for better security. To meet the design objective of easy-to-use and low-complexity computation, we integrate our proposed privacy-preserving techniques into one customized image filter. The image filter works in the raw image domain and does not require image format compliance. A highly integrated block could simplify the integration process to existing code. To improve the efficiency for the pixel-wise computation in our approach, we design and implement this customized image filter in the GPU via the OpenGL Shader. Shader is a program designed to run on some stage of a graphics processor, and written in the OpenGL Shading Language. We utilize the Fragment Shaders in the OpenGL rendering pipeline (after Rasterizer) for the pixel manipulation required in our proposed algorithm. The size covered by a fragment is related to the pixel area. Thus, the computationally intensive pixel-by-pixel operation could be converted to fragment processing with highly paralleled implementation in GPU. The reason that we utilize normalization and block-based processing in algorithm design is to fit the GPU Shader processing framework for high computation efficiency.
From Graphics to Visualization
Published in Alexandru Telea, Data Visualization, 2014
As explained in Section 2.2, OpenGL applies the rendering equation at a subset of the points of a given surface and uses the resulting illumination values to render the complete surface. The simplest, and least expensive, rendering model provided by OpenGL is flat shading. Given a polygonal surface, flat shading applies the lighting model (Equation (2.1)) only once for the complete polygon, e.g., for the center point, and then uses the resulting color to render the whole polygon surface. The polygon normal can be computed automatically by OpenGL from the polygon vertices. The polygon is assumed to be a flat surface, so its normal is constant. This implies a constant shading result following Equation (2.1), hence the name “flat shading.” In OpenGL, the flat shading mode is selected by the function call
The Effect of Interactive Cues on the Perception of Angiographic Volumes in Virtual Reality
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2021
Andrey Titov, Marta Kersten-Oertel, Simon Drouin
Shading is a photorealistic cue that simulates how an object reflects light when illuminated by a light source. One of the main advantages of this cue is that it is intuitive since it lets the viewer use knowledge about how objects are illuminated in real life. In the static version of shading, the light source is located at the midpoint between the two eyes, similarly to the light on a miner’s helmet. This way, the volume is always fully illuminated, no matter the position of the head in the virtual environment (see Figure 1(a)). In the dynamic version of shading, a point light source is attached to the tip of the pointer. Thus, as the user moves the pointer around the volume the anatomy around the pointer tip is illuminated and other parts of the volume fall into shadows. In other words, the light source works similarly to a match or flashlight that illuminates an object in a dark environment (see Figure 1(b)). The light source has a linear decay in intensity, which provides an additional cue for localisation of the pointer inside the volume. Shading was implemented using the Blinn-Phong reflection model (Blinn 1977)).