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--- fw:ogl:graphics [2013/02/10 18:24]
alfred [Shaders]
+++ fw:ogl:graphics [2020/05/09 09:25] (actual)
@@ Línea 15: / Línea 15: @@
 ==== Shaders ====
 Los shaders son programas que se ejecutan sobre el procesador gráfico y son utilizados para modificar los efectos de luz, sombras y producir efectos de postprocesado especiales. Proporcionan gran flexibilidad a la hora de programar la GPU.
-=== Tipos de shaders ===
-  * Vertex shaders
-Vertex shaders are run once for each vertex given to the graphics processor. The purpose is to transform each vertex's 3D position in virtual space to the 2D coordinate at which it appears on the screen (as well as a depth value for the Z-buffer). Vertex shaders can manipulate properties such as position, color, and texture coordinate, but cannot create new vertices. The output of the vertex shader goes to the next stage in the pipeline, which is either a geometry shader if present, or the pixel shader and rasterizer otherwise. Vertex shaders can enable powerful control over the details of position, movement, lighting, and color in any scene involving 3D models.
-  * Geometry shaders
-Geometry shaders are a relatively new type of shader, introduced in Direct3D 10 and OpenGL 3.2; formerly available in OpenGL 2.0+ with the use of extensions.[2] This type of shader can generate new graphics primitives, such as points, lines, and triangles, from those primitives that were sent to the beginning of the graphics pipeline.[3]
-Geometry shader programs are executed after vertex shaders. They take as input a whole primitive, possibly with adjacency information. For example, when operating on triangles, the three vertices are the geometry shader's input. The shader can then emit zero or more primitives, which are rasterized and their fragments ultimately passed to a pixel shader.
-Typical uses of a geometry shader include point sprite generation, geometry tessellation, shadow volume extrusion, and single pass rendering to a cube map. A typical real world example of the benefits of geometry shaders would be automatic mesh complexity modification. A series of line strips representing control points for a curve are passed to the geometry shader and depending on the complexity required the shader can automatically generate extra lines each of which provides a better approximation of a curve.
-  * Pixel shaders
+=== Tipos de shaders ===
-Pixel shaders, also known as fragment shaders, compute color and other attributes of each fragment. Pixel shaders range from always outputting the same color, to applying a lighting value, to doing bump mapping, shadows, specular highlights, translucency and other phenomena. They can alter the depth of the fragment (for Z-buffering), or output more than one color if multiple render targets are active. In 3D graphics, a pixel shader alone cannot produce very complex effects, because it operates only on a single fragment, without knowledge of a scene's geometry. However, pixel shaders do have knowledge of the screen coordinate being drawn, and can sample the screen and nearby pixels if the contents of the entire screen are passed as a texture to the shader. This technique can enable a wide variety of two-dimensional postprocessing effects, such as blur, or edge detection/enhancement for cartoon/cel shaders. Pixel shaders may also be applied in intermediate stages to any two-dimensional images in the pipeline, whereas vertex shaders always require a 3D model. For instance, a pixel shader is the only kind of shader that can act as a postprocessor or filter for a video stream after it has been rasterized.
+  * **Vertex shaders**: Se ejecutan por cada vértice. Su propósito es transformar cada vértice 3d en una coordenada 2d. Dan muchas facilidades para manipular sus propiedades (posición, color y textura) aunque no crear nuevos vértices.
+  * **Geomtry shaders**: Pueden generar nuevas primitivas gráficas (puntos, líneas, triangulos...). Se ejecutan después de los vertex sahders. Toman como input una primitiva. Entre sus usos está el de la generación de puntos de sprite, tessellation, volumen y extrusión de sombras... Un ejemplo sería el de la modificación de una malla compleja, se pueden generar puntos de control para una curva y generar líneas extra para aproximarla.
+  * **Pixel shaders** (también conocidos como **fragment shaders**): Tratan atributos como el color de cada fragmento. Para simplificar el valor de luz, hacer bump mapping, sombras, objetos translucidos... Pueden alterar la profundidad de los fragmentos o sacar más de un color si han sido activados múltiples targets de render. Aunque no pueden aplicar grandes alteraciones, a su nivel se conoce las coordenadas de la pantalla donde donde serán dibujados y los pixels vecinos, cosa que permite ejecutar gran variedad de efectos de postprocesado 2d (como blur, detección y acentuación de bordes...).
 === Algoritmos de shading ===
@@ Línea 46: / Línea 41: @@
   * **HLSL**: Oficial de Direct3d (High Level Shading Language).
   * **Cg**: Propio de nVidia.
-===== GLSL =====
+===== Notas =====
+  * [[http://es.wikipedia.org/wiki/Coordenadas_homog%C3%A9neas]]

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