glBlendFuncGLSRCALPHA

glBlendFuncGLSRCALPHA refers to using the OpenGL blending source factor GL_SRC_ALPHA in the blending equation defined by glBlendFunc. Blending combines the incoming fragment color (the source) with the color already stored in the framebuffer (the destination) when blending is enabled. glBlendFunc takes two factors: the source factor and the destination factor, chosen from symbolic constants such as GL_SRC_ALPHA and GL_ONE_MINUS_SRC_ALPHA.

The common form is glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA). This implements standard alpha blending for non-premultiplied alpha textures. The resulting color is computed as: sourceColor multiplied by the source alpha, plus the destination color multiplied by (1 minus the source alpha). The alpha channel is blended using the same factors, yielding resultAlpha = srcAlpha * srcAlpha + dstAlpha * (1 - srcAlpha). This behavior is defined for all channels unless overridden by separate factors.

Practical considerations include enabling blending with glEnable(GL_BLEND) and optionally controlling the blend equation with glBlendEquation (default is GL_FUNC_ADD). If textures are premultiplied with alpha, a different pairing—glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA)—is recommended for correct results. For more control, glBlendFuncSeparate allows specifying different factors for color and alpha channels.

Common pitfalls involve drawing order and depth testing. Blended fragments require careful ordering (typically back-to-front) and, depending on the scene, may require enabling or disabling depth writes. Understanding whether textures use premultiplied alpha is important for choosing the appropriate blend factors.