Function glTexImage2D

Texturing allows elements of an image array to be read by shaders.

To define texture images, call glTexImage2D. The arguments describe the parameters of the texture image, such as height, width, width of the border, level-of-detail number (see glTexParameter), and number of color components provided. The last three arguments describe how the image is represented in memory.

If target is GL_PROXY_TEXTURE_2D, GL_PROXY_TEXTURE_1D_ARRAY, GL_PROXY_TEXTURE_CUBE_MAP, or GL_PROXY_TEXTURE_RECTANGLE, no data is read from data, but all of the texture image state is recalculated, checked for consistency, and checked against the implementation's capabilities. If the implementation cannot handle a texture of the requested texture size, it sets all of the image state to 0, but does not generate an error (see glGetError). To query for an entire mipmap array, use an image array level greater than or equal to 1.

If target is GL_TEXTURE_2D, GL_TEXTURE_RECTANGLE or one of the GL_TEXTURE_CUBE_MAP targets, data is read from data as a sequence of signed or unsigned bytes, shorts, or longs, or single-precision floating-point values, depending on type. These values are grouped into sets of one, two, three, or four values, depending on format, to form elements. Each data byte is treated as eight 1-bit elements, with bit ordering determined by GL_UNPACK_LSB_FIRST (see glPixelStore).

If target is GL_TEXTURE_1D_ARRAY, data is interpreted as an array of one-dimensional images.

If a non-zero named buffer object is bound to the GL_PIXEL_UNPACK_BUFFER target (see glBindBuffer) while a texture image is specified, data is treated as a byte offset into the buffer object's data store.

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_RED Each element is a single red component. The GL converts it to floating point and assembles it into an RGBA element by attaching 0 for green and blue, and 1 for alpha. Each component is clamped to the range [0,1].

• GL_RG Each element is a single red/green double The GL converts it to floating point and assembles it into an RGBA element by attaching 0 for blue, and 1 for alpha. Each component is clamped to the range [0,1].

• GL_RGB, GL_BGR 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 clamped to the range [0,1].

• GL_RGBA, GL_BGRA Each element contains all four components. Each component is clamped to the range [0,1].

• GL_DEPTH_COMPONENT Each element is a single depth value. The GL converts it to floating point and clamps to the range [0,1].

• GL_DEPTH_STENCIL Each element is a pair of depth and stencil values. The depth component of the pair is interpreted as in GL_DEPTH_COMPONENT. The stencil component is interpreted based on specified the depth + stencil internal format.

If an application wants to store the texture at a certain resolution or in a certain format, it can request the resolution and format with internalFormat. The GL will choose an internal representation that closely approximates that requested by internalFormat, but it may not match exactly. (The representations specified by GL_RED, GL_RG, GL_RGB, and GL_RGBA must match exactly.)

If the internalFormat parameter is one of the generic compressed formats, GL_COMPRESSED_RED, GL_COMPRESSED_RG, GL_COMPRESSED_RGB, or GL_COMPRESSED_RGBA, the GL will replace the internal format with the symbolic constant for a specific internal format and compress the texture before storage. If no corresponding internal format is available, or the GL can not compress that image for any reason, the internal format is instead replaced with a corresponding base internal format.

If the internalFormat parameter is GL_SRGB, GL_SRGB8, GL_SRGB_ALPHA, or GL_SRGB8_ALPHA8, the texture is treated as if the red, green, or blue components are encoded in the sRGB color space. Any alpha component is left unchanged. The conversion from the sRGB encoded component 𝐜ₛ to a linear component 𝐜ₗ is:

ㅤㅤ⎧ 𝐜ₛ / 12.92ㅤㅤㅤㅤㅤㅤㅤif 𝐜ₛ ≤ 0.04045

𝐜ₗ = ⎨

ㅤㅤ⎩ (𝐜ₛ + 0.055 / 1.055)²·⁴ㅤㅤif 𝐜ₛ > 0.04045

Assume 𝐜ₛ is the sRGB component in the range [0,1].

Use the GL_PROXY_TEXTURE_2D, GL_PROXY_TEXTURE_1D_ARRAY, GL_PROXY_TEXTURE_RECTANGLE, or GL_PROXY_TEXTURE_CUBE_MAP target to try out a resolution and format. The implementation will update and recompute its best match for the requested storage resolution and format. To then query this state, call glGetTexLevelParameter. If the texture cannot be accommodated, texture state is set to 0.

A one-component texture image uses only the red component of the RGBA color extracted from data. A two-component image uses the R and G values. A three-component image uses the R, G, and B values. A four-component image uses all of the RGBA components.

Image-based shadowing can be enabled by comparing texture r coordinates to depth texture values to generate a boolean result. See glTexParameter for details on texture comparison.

Summary

specify a two-dimensional texture image

Example

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.
let texture_map: GLuint;
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.
let depth_texture: GLuint;
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.
let framebuffer: GLuint;
glGenFramebuffers(1, framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, 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);

let status: GLenum = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (status != GL_FRAMEBUFFER_COMPLETE)
    // Error

glBindFramebuffer(GL_FRAMEBUFFER, 0);
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Example

Create a texture object with linear mipmaps and edge clamping.

let texture_id: GLuint;
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() instead

glBindTexture(GL_TEXTURE_2D, 0);
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Tutorial

Songho - OpenGL Frame Buffer Object (FBO)

Tutorial

open.gl - Framebuffers

Tutorial

open.gl - Textures Objects and Parameters

Tutorial

opengl-tutorial.org - Tutorial 14 : Render To Texture

Tutorial

opengl-tutorial.org - Tutorial 16 : Shadow mapping

Tutorial

opengl-tutorial.org - Tutorial 5 : A Textured Cube

See

glTexImage2D