glTexImage2D 函数详解
glTexImage2D 函数详解
参考
glTexImage2D
glTexImage2D — specify a two-dimensional texture image
C Specification
void glTexImage2D( GLenum target,
GLint level,
GLint internalformat,
GLsizei width,
GLsizei height,
GLint border,
GLenum format,
GLenum type,
const GLvoid * data);
Parameters
target
Specifies the target texture of the active texture unit. Must be GL_TEXTURE_2D, GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X, GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, GL_TEXTURE_CUBE_MAP_POSITIVE_Z, or GL_TEXTURE_CUBE_MAP_NEGATIVE_Z.
level
Specifies the level-of-detail number. Level 0 is the base image level. Level n is the nth mipmap reduction image.
internalformat
Specifies the internal format of the texture. Must be one of the following symbolic constants: GL_ALPHA, GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB, GL_RGBA.
width
Specifies the width of the texture image. All implementations support 2D texture images that are at least 64 texels wide and cube-mapped texture images that are at least 16 texels wide.
height
Specifies the height of the texture image All implementations support 2D texture images that are at least 64 texels high and cube-mapped texture images that are at least 16 texels high.
border
Specifies the width of the border. Must be 0.
format
Specifies the format of the texel data. Must match internalformat. The following symbolic values are accepted: GL_ALPHA, GL_RGB, GL_RGBA, GL_LUMINANCE, and GL_LUMINANCE_ALPHA.
type
Specifies the data type of the texel data. The following symbolic values are accepted: GL_UNSIGNED_BYTE, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_4_4_4_4, and GL_UNSIGNED_SHORT_5_5_5_1.
data
Specifies a pointer to the image data in memory.
Description
Texturing maps a portion of a specified texture image onto each graphical primitive for which texturing is active. Texturing is active when the current fragment shader or vertex shader makes use of built-in texture lookup functions.
To define texture images, call glTexImage2D. The arguments describe the parameters of the texture image, such as height, width, level-of-detail number (see glTexParameter), and format. The last three arguments describe how the image is represented in memory.
Data is read from data as a sequence of unsigned bytes or shorts, depending on type. When type is GL_UNSIGNED_BYTE, each of the bytes is interpreted as one color component. When type is one of GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_4_4_4_4, or GL_UNSIGNED_SHORT_5_5_5_1, each unsigned short value is interpreted as containing all the components for a single texel, with the color components arranged according to format. Color components are treated as groups of one, two, three, or four values, again based on format. Groups of components are referred to as texels.
width×height texels are read from memory, starting at location data. By default, these texels are taken from adjacent memory locations, except that after all width texels are read, the read pointer is advanced to the next four-byte boundary. The four-byte row alignment is specified by glPixelStorei with argument GL_UNPACK_ALIGNMENT, and it can be set to one, two, four, or eight bytes.
The first element corresponds to the lower left corner of the texture image. Subsequent elements progress left-to-right through the remaining texels in the lowest row of the texture image, and then in successively higher rows of the texture image. The final element corresponds to the upper right corner of the texture image.
format determines the composition of each element in data. It can assume one of these symbolic values:
GL_ALPHA
Each element is a single alpha component. The GL converts it to floating point and assembles it into an RGBA element by attaching 0 for red, green, and blue. Each component is then clamped to the range [0,1].
GL_RGB
Each element is an RGB triple. The GL converts it to floating point and assembles it into an RGBA element by attaching 1 for alpha. Each component is then clamped to the range [0,1].
GL_RGBA
Each element contains all four components. The GL converts it to floating point, then each component is clamped to the range [0,1].
GL_LUMINANCE
Each element is a single luminance value. The GL converts it to floating point, then assembles it into an RGBA element by replicating the luminance value three times for red, green, and blue and attaching 1 for alpha. Each component is then clamped to the range [0,1].
GL_LUMINANCE_ALPHA
Each element is a luminance/alpha pair. The GL converts it to floating point, then assembles it into an RGBA element by replicating the luminance value three times for red, green, and blue. Each component is then clamped to the range [0,1].
Color components are converted to floating point based on the type. When type is GL_UNSIGNED_BYTE, each component is divided by 28−1. When type is GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_4_4_4_4, or GL_UNSIGNED_SHORT_5_5_5_1, each component is divided by 2N−1, where N is the number of bits in the bitfield.
Notes
internalformat must match format. No conversion between formats is supported during texture image processing. type may be used as a hint to specify how much precision is desired, but a GL implementation may choose to store the texture array at any internal resolution it chooses.
data may be a null pointer. In this case, texture memory is allocated to accommodate a texture of width width and height height. You can then download subtextures to initialize this texture memory. The image is undefined if the user tries to apply an uninitialized portion of the texture image to a primitive.
glTexImage2D specifies a two-dimensional or cube-map texture for the current texture unit, specified with glActiveTexture.
Errors
GL_INVALID_ENUM is generated if target is not GL_TEXTURE_2D, GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X, GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, GL_TEXTURE_CUBE_MAP_POSITIVE_Z, or GL_TEXTURE_CUBE_MAP_NEGATIVE_Z.
GL_INVALID_ENUM is generated if format or type is not an accepted value.
GL_INVALID_VALUE is generated if target is one of the six cube map 2D image targets and the width and height parameters are not equal.
GL_INVALID_VALUE is generated if level is less than 0.
GL_INVALID_VALUE may be generated if level is greater than log2(max), where max is the returned value of GL_MAX_TEXTURE_SIZE when target is GL_TEXTURE_2D or GL_MAX_CUBE_MAP_TEXTURE_SIZE when target is not GL_TEXTURE_2D.
GL_INVALID_VALUE is generated if internalformat is not an accepted format.
GL_INVALID_VALUE is generated if width or height is less than 0 or greater than GL_MAX_TEXTURE_SIZE when target is GL_TEXTURE_2D or GL_MAX_CUBE_MAP_TEXTURE_SIZE when target is not GL_TEXTURE_2D.
GL_INVALID_VALUE is generated if border is not 0.
GL_INVALID_OPERATION is generated if format does not match internalformat.
GL_INVALID_OPERATION is generated if type is GL_UNSIGNED_SHORT_5_6_5 and format is not GL_RGB.
GL_INVALID_OPERATION is generated if type is GL_UNSIGNED_SHORT_4_4_4_4 or GL_UNSIGNED_SHORT_5_5_5_1 and format is not GL_RGBA.
Associated Gets
glGet with argument GL_MAX_TEXTURE_SIZE or GL_MAX_CUBE_MAP_TEXTURE_SIZE
Examples
Create a framebuffer object with a texture-based color attachment and a texture-based depth attachment. Using texture-based attachments allows sampling of those textures in shaders.
// fbo_width and fbo_height are the desired width and height of the FBO.
// For Opengl <= 4.4 or if the GL_ARB_texture_non_power_of_two extension
// is present, fbo_width and fbo_height can be values other than 2^n for
// some integer n.
// Build the texture that will serve as the color attachment for the framebuffer.
GLuint texture_map;
glGenTextures(1, &texture_map);
glBindTexture(GL_TEXTURE_2D, texture_map);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, fbo_width, fbo_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
// Build the texture that will serve as the depth attachment for the framebuffer.
GLuint depth_texture;
glGenTextures(1, &depth_texture);
glBindTexture(GL_TEXTURE_2D, depth_texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, fbo_width, fbo_height, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
// Build the framebuffer.
GLuint framebuffer;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, (GLuint)framebuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture_map, 0);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depth_texture, 0);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (status != GL_FRAMEBUFFER_COMPLETE)
// Error
glBindFramebuffer(GL_FRAMEBUFFER, 0);
Create a texture object with linear mipmaps and edge clamping.
GLuint texture_id;
glGenTextures(1, &texture_id);
glBindTexture(GL_TEXTURE_2D, texture_id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
// texture_data is the source data of your texture, in this case
// its size is sizeof(unsigned char) * texture_width * texture_height * 4
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texture_width, texture_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, texture_data);
glGenerateMipmap(GL_TEXTURE_2D); // Unavailable in OpenGL 2.1, use gluBuild2DMipmaps() insteads.
glBindTexture(GL_TEXTURE_2D, 0);
Tutorials
Songho - OpenGL Frame Buffer Object (FBO)
open.gl - Framebuffers
open.gl - Textures Objects and Parameters
opengl-tutorial.org - Tutorial 14 : Render To Texture
opengl-tutorial.org - Tutorial 16 : Shadow mapping
opengl-tutorial.org - Tutorial 5 : A Textured Cube
See Also
glActiveTexture, glCompressedTexImage2D, glCompressedTexSubImage2D, glCopyTexImage2D, glCopyTexSubImage2D, glPixelStorei, glTexSubImage2D, glTexParameter
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/.
Thin
glTexImage2D
http://docs.gl/es2/glTexImage2D
glTexImage2D - 指定一个二维纹理图像
C规范
void glTexImage2D(
GLenum target，
GLint level，
GLint internalformat，
GLsizei 宽度，
GLsizei 高度，
GLint 边框，
GLenum format，
GLenum type，
const GLvoid * data) ;
internalFormat：指定OpenGL是如何管理纹理单元中数据格式的，但是有很多解释说这个参数必须和后面的format参数一样，这样理解笔者认为有点不太合适！笔者认为应该理解为internalFormat和format必须一致。
internalforamt指的是纹理数据在OpenGL中是如何表示的，如GL_RGB就表示纹理的像素在OpenGL里面以红绿蓝三个分量表示，
format指的是载入纹理的格式，它告诉OpenGL外部数据是如何存储每个像素数据的。
参数
target
指定活动纹理单元的目标纹理。必须是GL_TEXTURE_2D，GL_TEXTURE_CUBE_MAP_POSITIVE_X，GL_TEXTURE_CUBE_MAP_NEGATIVE_X，GL_TEXTURE_CUBE_MAP_POSITIVE_Y，GL_TEXTURE_CUBE_MAP_NEGATIVE_Y，GL_TEXTURE_CUBE_MAP_POSITIVE_Z，或GL_TEXTURE_CUBE_MAP_NEGATIVE_Z。
level
指定详细程度编号。级别0是基本图像级别。级别n是第n个缩略图缩小图像。
internalformat
指定纹理的内部格式。必须是下列符号常量之一：GL_ALPHA，GL_LUMINANCE，GL_LUMINANCE_ALPHA，GL_RGB，GL_RGBA。
width
指定纹理图像的宽度。所有实现都支持宽度至少为64 texels的2D纹理图像和宽度至少为16 texels的立方体贴图纹理图像。
height
指定纹理图像的高度所有实现都支持至少64像素高的2D纹理图像和至少16像素高的立方体贴图纹理图像。
border
指定边框的宽度。必须为0。
format
指定纹理数据的格式。必须匹配internalformat。下面的符号值被接受：GL_ALPHA，GL_RGB，GL_RGBA，GL_LUMINANCE，和GL_LUMINANCE_ALPHA。
type
指定纹理数据的数据类型。下面的符号值被接受：GL_UNSIGNED_BYTE，GL_UNSIGNED_SHORT_5_6_5，GL_UNSIGNED_SHORT_4_4_4_4，和GL_UNSIGNED_SHORT_5_5_5_1。
data
指定一个指向内存中图像数据的指针。
描述
纹理将指定纹理图像的一部分映射到纹理化为活动的每个图形基元上。当前片段着色器或顶点着色器使用内置纹理查找函数时，纹理处于活动状态。
要定义纹理图像，请调用glTexImage2D。参数描述纹理图像的参数，如高度，宽度，细节层次数（参见glTexParameter）和格式。最后三个参数描述了图像在内存中的表示方式。
数据从data一系列无符号字节或短路中读取，具体取决于type。当type是GL_UNSIGNED_BYTE，每个字节被解释为一个颜色分量。当type是中的一个GL_UNSIGNED_SHORT_5_6_5，GL_UNSIGNED_SHORT_4_4_4_4或GL_UNSIGNED_SHORT_5_5_5_1，各无符号短值被解释为包含所有组件用于单个纹素，利用根据设置在颜色分量format。颜色分量被视为一个，两个，三个或四个值的组，也是基于format。组件组被称为纹理元素。
width×height
texels are read from memory, starting at location data. By default, these texels are taken from adjacent memory locations, except that after all width texels are read, the read pointer is advanced to the next four-byte boundary. The four-byte row alignment is specified by glPixelStorei with argument GL_UNPACK_ALIGNMENT, and it can be set to one, two, four, or eight bytes.
internalformat必须匹配format。在纹理图像处理过程中不支持格式间的转换。type可以用作提示来指定需要多少精度，但是GL实现可以选择以其选择的任何内部分辨率来存储纹理数组。
data可能是一个空指针。在这种情况下，会分配纹理内存以适应宽度width和高度的纹理height。然后你可以下载子文本来初始化这个纹理内存。如果用户尝试将纹理图像的未初始化部分应用于基元，则图像未定义。
此函数比较迷惑的地方是internalformat和format
internalformat 指定了颜色都有那些成分构成 如RGB表示颜色组成由Red分量Green分量Blue分量构成，RGBA表示颜色组成由Red分量Green分量Blue分量Alpha分量构成。
format 表示了颜色数据分量在内存中的数据存储格式。
如 RGBA(对于大端对齐的CPU) ABGR(对于小端对齐的CPU)表示颜色在内存中的排列方式如下：
如 ARGB(对于大端对齐的CPU) BGRA(对于小端对齐的CPU)表示颜色在内存中的排列方式如下：
就是说format指定的是颜色分量在内存中的数据存储格式。
根据openGL es2.0 的官方文档 format Must match internalformat. 此处所说的must match 我认为应该理解为必须一致，而不是必须一样，一致说的是指定的RGBA的格式一致。
官方的openGL es 2.0和3.0的文档表明，openGLes并不支持GL_BGRA类型的format，而opengl是支持GL_BGRA类型的format的。但是笔者在iOS6以上的设备上测试发现，
iOS6以上的设备是支持format格式为GL_BGRA，或许是iOS对此函数进行了扩展。
opengl es 2.0 http://docs.gl/es2/glTexImage2D
opengl 2.0 http://docs.gl/gl2/glTexImage2D
例子 使用基于纹理的颜色附件和基于纹理的深度附件创建帧缓冲区对象。使用基于纹理的附件可以对着色器中的纹理进行采样。
// fbo_width and fbo_height are the desired width and height of the FBO.
// For Opengl <= 4.4 or if the GL_ARB_texture_non_power_of_two extension
// is present, fbo_width and fbo_height can be values other than 2^n for
// some integer n.
// Build the texture that will serve as the color attachment for the framebuffer.
GLuint texture_map;
glGenTextures(1, &texture_map);
glBindTexture(GL_TEXTURE_2D, texture_map);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, fbo_width, fbo_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
// Build the texture that will serve as the depth attachment for the framebuffer.
GLuint depth_texture;
glGenTextures(1, &depth_texture);
glBindTexture(GL_TEXTURE_2D, depth_texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, fbo_width, fbo_height, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
// Build the framebuffer.
GLuint framebuffer;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, (GLuint)framebuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture_map, 0);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depth_texture, 0);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (status != GL_FRAMEBUFFER_COMPLETE)
// Error
glBindFramebuffer(GL_FRAMEBUFFER, 0);
创建一个纹理对象使用mipmap和edge clamping来创建
GLuint texture_id;
glGenTextures(1, &texture_id);
glBindTexture(GL_TEXTURE_2D, texture_id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
// texture_data is the source data of your texture, in this case
// its size is sizeof(unsigned char) * texture_width * texture_height * 4
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texture_width, texture_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, texture_data);
glGenerateMipmap(GL_TEXTURE_2D); // Unavailable in OpenGL 2.1, use gluBuild2DMipmaps() insteads.
glBindTexture(GL_TEXTURE_2D, 0);