Textures

GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);

// Upload image data
glTexImage2D(GL_TEXTURE_2D, /*mip=*/0, GL_RGBA8,
             width, height, /*border=*/0,
             GL_RGBA, GL_UNSIGNED_BYTE, pixels);

glGenerateMipmap(GL_TEXTURE_2D); // auto-generate all mip levels

GLuint tex;
glCreateTextures(GL_TEXTURE_2D, 1, &tex);

// Immutable storage — format and dimensions fixed (recommended)
glTextureStorage2D(tex, mipLevels, GL_RGBA8, width, height);
glTextureSubImage2D(tex, /*mip=*/0, /*x=*/0, /*y=*/0,
                    width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
glGenerateTextureMipmap(tex);

// Upload pre-compressed data
glCompressedTexImage2D(GL_TEXTURE_2D, mip, internalFormat,
                       width, height, 0, imageSize, data);

// Wrapping
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
// DSA: glTextureParameteri(tex, GL_TEXTURE_WRAP_S, GL_REPEAT);

// Filtering
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

// Border color (used with GL_CLAMP_TO_BORDER)
float border[] = { 0.0f, 0.0f, 0.0f, 1.0f };
glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, border);

// Anisotropic filtering (widely supported, core in GL 4.6)
float maxAniso;
glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY, &maxAniso);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY, maxAniso);

// LOD clamp
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_LOD, 0.0f);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_LOD, 1000.0f); // default
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_LOD_BIAS, -0.5f);  // sharper

// Swizzle (remap channels)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_R, GL_RED);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_G, GL_GREEN);
// or all at once
GLint swiz[] = { GL_RED, GL_RED, GL_RED, GL_ONE }; // R as grayscale
glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_RGBA, swiz);

// Mip range
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 8);

// Activate unit and bind
glActiveTexture(GL_TEXTURE0 + unit);  // unit = 0..GL_MAX_TEXTURE_IMAGE_UNITS-1
glBindTexture(GL_TEXTURE_2D, tex);

// Set sampler uniform to the unit index
glUniform1i(glGetUniformLocation(prog, "uAlbedo"), unit);

// DSA binding (GL 4.5+)
glBindTextureUnit(unit, tex);  // no glActiveTexture needed

GLuint sampler;
glGenSamplers(1, &sampler);
glSamplerParameteri(sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glSamplerParameteri(sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glSamplerParameteri(sampler, GL_TEXTURE_WRAP_S, GL_REPEAT);
glSamplerParameterf(sampler, GL_TEXTURE_MAX_ANISOTROPY, 16.0f);

glBindSampler(unit, sampler);  // sampler overrides texture's own params
glDeleteSamplers(1, &sampler);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LESS);
// Returns 0.0 or 1.0 (or filtered PCF result) from sampler2DShadow

uniform sampler2DShadow uShadowMap;
float shadow = texture(uShadowMap, vec3(uv, compareDepth));

glCreateTextures(GL_TEXTURE_CUBE_MAP, 1, &tex);
glTextureStorage2D(tex, mips, GL_RGB8, width, height);

// Upload each face
GLenum faces[] = {
    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, GL_TEXTURE_CUBE_MAP_NEGATIVE_Z
};
for (int i = 0; i < 6; i++) {
    // Can use glTextureSubImage3D with zoffset=i for cube maps
    glTextureSubImage3D(tex, 0, 0, 0, i, width, height, 1,
                        GL_RGB, GL_UNSIGNED_BYTE, faceData[i]);
}
glTextureParameteri(tex, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTextureParameteri(tex, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTextureParameteri(tex, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

uniform samplerCube uCubemap;
vec3 color = texture(uCubemap, direction).rgb;

glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &tex);
glTextureStorage3D(tex, mips, GL_RGBA8, width, height, layerCount);
glTextureSubImage3D(tex, 0, 0, 0, layer, width, height, 1,
                    GL_RGBA, GL_UNSIGNED_BYTE, data);

uniform sampler2DArray uAtlas;
vec4 color = texture(uAtlas, vec3(uv, float(tileIndex)));

// Bind a texture level to an image unit for shader read/write
glBindImageTexture(
    /*unit=*/0, tex, /*level=*/0,
    /*layered=*/GL_FALSE, /*layer=*/0,
    GL_READ_WRITE,    // GL_READ_ONLY, GL_WRITE_ONLY, GL_READ_WRITE
    GL_RGBA32F        // must match texture internal format
);

layout(rgba32f, binding = 0) uniform image2D uImage;
vec4 v = imageLoad(uImage, ivec2(gl_GlobalInvocationID.xy));
imageStore(uImage, ivec2(gl_GlobalInvocationID.xy), v * 2.0);

// Readback (slow — causes pipeline stall)
glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

// Async readback with PBO
glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
glReadPixels(x, y, w, h, GL_RGBA, GL_UNSIGNED_BYTE, 0); // 0 = offset into PBO
// ... next frame ...
void* ptr = glMapBuffer(GL_PIXEL_PACK_BUFFER, GL_READ_ONLY);
memcpy(dest, ptr, size);
glUnmapBuffer(GL_PIXEL_PACK_BUFFER);

// Async upload with PBO
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
glTextureSubImage2D(tex, 0, 0, 0, w, h, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);

GLuint64 handle = glGetTextureHandleARB(tex);
glMakeTextureHandleResidentARB(handle);

// Pass handle to shader via uniform/SSBO
glUniformHandleui64ARB(loc, handle);

#extension GL_ARB_bindless_texture : enable
layout(location = 0) uniform sampler2D uTex; // handle passed as uvec2 internally