OpenGL ES 1.0 规范详解

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"gles的描述文档，主要涵盖了OpenGL ES (OpenGL for Embedded Systems)的相关内容，这是一个专注于嵌入式系统的图形库标准。此文档可能是OpenGL ES规范的版本1.0.0的注解版，由David Blythe编辑，并由Khronos Group Inc.发布和持有版权。文档详细阐述了OpenGL ES的接口、功能以及使用规定。" OpenGL ES是OpenGL的一个子集，设计用于嵌入式设备，如移动设备和智能硬件，它提供了在这些平台上的2D和3D图形渲染能力。OpenGL ES规范定义了一组API（应用程序编程接口），使得开发者能够创建复杂的图形应用程序，包括游戏、地图应用和其他需要高质量视觉效果的应用。该规范强调了效率和资源管理，因为在嵌入式系统中，处理能力和内存通常比桌面系统更为有限。OpenGL ES支持顶点数组、纹理、着色器语言（如GLSL ES）、深度测试、模板测试等特性，这些都是实现高级图形效果的基础。 OpenGL ES有多个版本，每个版本都增加了新的特性和改进。版本1.0.0可能是早期版本，可能不包含后来版本中的一些高级特性，例如着色器支持可能较为基础。随着时间的推移，OpenGL ES经历了多个版本迭代，例如2.0引入了顶点和片段着色器，3.0则引入更多现代图形特性，如几何着色器和多采样抗锯齿。在实际开发中，遵循OpenGL ES的规范是至关重要的，因为它确保了跨平台的兼容性。开发者可以利用OpenGL ES API来创建跨设备运行的应用，只要目标平台支持相应的OpenGL ES版本。同时，由于Khronos Group的版权规定，未经许可，不得修改或以任何形式分发该规范，但成员可以无费用地复制和分发未修改的版本。为了实施OpenGL ES，开发者需要理解并遵循规范中的详细说明，包括数据类型、函数调用、状态管理和错误处理。此外，还需要掌握与之配合的工具和库，如图形调试器和性能分析器，以便于优化图形性能和找出潜在问题。 OpenGL ES是嵌入式系统图形开发的关键技术，提供了强大而灵活的图形渲染能力。通过深入学习和实践OpenGL ES规范，开发者可以创建出在各种嵌入式设备上表现出色的图形应用程序。

10 OpenGL Operation

2.13 Colors and Coloring

The OpenGL 1.3 lighting model is supported with the following exceptions: no support for the color index

lighting, secondary color, different front and back materials, local viewer, or color material mode other than

AMBIENT AND DIFFUSE.

Directional, positional, and spot lights are all supported. An implementation must support a minimum

of 8 lights. The Material command cannot independently change the front and back face properties, so the

result is that materials always have the same front and back properties. Two-sided lighting is supported,

though the front and back material properties used in the lighting computation will also be equal. The

ColorMaterial command is not supported, so the color material mode cannot be changed from the default

AMBIENT AND DIFFUSE mode, though COLOR MATERIAL can be enabled in this mode. Neither local view-

ing computations nor separate specular color computation can be enabled using the LightModel command,

therefore only the OpenGL 1.3 default inﬁnite viewer and single color computational models are supported.

Smooth and ﬂat shading are fully supported for all primitives.

OpenGL 1.3 Common Common-Lite

FrontFace(enum mode)  

Enable/Disable(LIGHTING)  

Enable/Disable(LIGHT{0-7})  

Materialf[v](enum face, enum pname, T param)

face = FRONT AND BACK  †

face = FRONT,BACK – –

pname = AMBIENT,DIFFUSE,SPECULAR,EMISSION,SHININESS  †

pname = AMBIENT AND DIFFUSE  †

pname = COLOR INDEXES – –

Materiali[v](enum face, enum pname, T param) – –

GetMaterial{if}[v](enum face, enum pname, T

params) – –

Lightf[v](enum light, enum pname, T param)  †

Lighti[v](enum light, enum pname, T param) – –

GetLight{if}[v](enum light, enum pname, T

params) – –

LightModelf[v](enum pname, T param)

pname = LIGHT MODEL TWO SIDE  †

pname = LIGHT MODEL AMBIENT  †

pname = LIGHT MODEL COLOR CONTROL – –

pname = LIGHT MODEL LOCAL VIEWER – –

LightModeli[v](enum pname, T param) – –

Enable/Disable(COLOR MATERIAL) 

‡



‡

ColorMaterial(enum face, enum mode) – –

ShadeModel(enum mode)  

■ Lighting is a desirable feature, so as much as possible is included in the Common and Common-

Lite proﬁles. The minimum number of lights is not reduced since reducing it only saves memory for

the state and the savings is not signiﬁcant unless it is greatly reduced. The number cannot be greatly

reduced (e.g., to 1 or 2) as many applications need three or more lights. Support for secondary color

Rasterization 13

OpenGL 1.3 Common Common-Lite

LineWidth(float width)  †

Enable/Disable(LINE SMOOTH)  

LineStipple(int factor, ushort pattern) – –

Enable/Disable(LINE STIPPLE) – –

■ Antialiasing is important for visual quality, particularly for devices with low spatial resolution (pix-

els per mm). Some antialiasing can be implemented within the application using 2D textures, but

antialiasing is used by enough applications that it should be in the proﬁle rather than something left

to the application. The OpenGL 1.3 point and line antialiasing requirements provide substantial im-

plementation latitude. In particular, only size/width 1.0 is required to be supported and the coverage

computation constraints are easily satisﬁed. Line stippling is also used by ”presentation graphics”

and engineering applications. It can be implemented by the application, and the implementation cost

is considered too high to include in the proﬁle. ❑

3.5 Polygons

Polygonal geometry support is reduced to triangle strips, triangle fans and independent triangles. All raster-

ization modes are supported except for point and line PolygonMode and antialiased polygons using polygon

smooth. Depth offset is supported in FILL mode only.

OpenGL 1.3 Common Common-Lite

CullFace(enum mode)  

Enable/Disable(CULL FACE)  

PolygonMode(enum face, enum mode) – –

Enable/Disable(POLYGON SMOOTH) – –

PolygonStipple(const ubyte

mask) – –

GetPolygonStipple(ubyte

mask) – –

Enable/Disable(POLYGON STIPPLE) – –

PolygonOffset(float factor, float units)  †

Enable/Disable(enum cap)

cap = POLYGON OFFSET FILL  

cap = POLYGON OFFSET LINE, POLYGON OFFSET POINT – –

■ Support for all triangle types (independents, strips, fans) is not overly burdensome and each type

has some desirable utility: strips for general performance and applicability, independents for efﬁciently

specifying unshared vertex attributes, and fans for representing ”corner-turning” geometry. Face

culling is important for eliminating unnecessary rasterization. Polygon stipple is desirable for doing

patterned ﬁlls for ”presentation graphics”. It is also useful for transparency, but support for alpha is

sufﬁcient for that. Polygon stippling does represent a large burden for the polygon rasterization path

and can usually be emulated using texture mapping and alpha test, so it is omitted. Polygon offset for

ﬁlled triangles is necessary for rendering coplanar and outline polygons and if not present requires

either stencil buffers or application tricks. Antialiased polygons using POLYGON SMOOTH is just as

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