GLLIGHTMODEL(3G)

✨ GLLIGHTMODEL 💡 — the 3G manual page, but make it make sense

okay bestie, sit DOWN, because today we're setting the lighting model parameters and it's giving main character energy for your entire scene. 🎀

---

🌸 NAME 🌸

glLightModelf, glLightModeli, glLightModelfv... no wait, it's glLightModelfv, glLightModeliv — set the lighting model parameters. literally the four functions that decide how your whole vibe gets lit. 💅

---

🫶 C SPECIFICATION 🫶

void glLightModelf( GLenum pname,
                    GLfloat param )
void glLightModeli( GLenum pname,
                    GLint param )

---

🧚 PARAMETERS 🧚

• pname — specifies a single-valued lighting model parameter, bestie. The accepted ones are GL_LIGHT_MODEL_LOCAL_VIEWER, GL_LIGHT_MODEL_COLOR_CONTROL, and GL_LIGHT_MODEL_TWO_SIDE. that's the list, no extras. ✨
• param — specifies the value that param will be set to. (yes it says it like that. iconic self-reference tbh.) 💀

---

🦋 C SPECIFICATION 🦋

round two, and this time there's a pointer involved 🫶

void glLightModelfv( GLenum pname,
                     const GLfloat *params )
void glLightModeliv( GLenum pname,
                     const GLint *params )

---

💜 PARAMETERS 💜

• pname — specifies a lighting model parameter (plural energy now, not just single-valued). Accepted here: GL_LIGHT_MODEL_AMBIENT, GL_LIGHT_MODEL_COLOR_CONTROL, GL_LIGHT_MODEL_LOCAL_VIEWER, and GL_LIGHT_MODEL_TWO_SIDE. 🌈
• params — specifies a pointer to the value or values that params will be set to. pointer bestie, we love her. 🍓

---

👑 DESCRIPTION 👑

glLightModel sets the lighting model parameter. pname names a parameter and params gives the new value. There are three lighting model parameters — well, four if you count color control, but the original says three and then lists four, and honestly? slay, we don't gatekeep. 💅

• GL_LIGHT_MODEL_AMBIENT — params contains four integer or floating-point values that specify the ambient RGBA intensity of the entire scene. Integer values are mapped linearly such that the most positive representable value maps to 1.0, and the most negative representable value maps to -1.0. Floating-point values are mapped directly. Neither integer nor floating-point values are clamped — no vibe check, no correction, she takes what you give her. The initial ambient scene intensity is (0.2, 0.2, 0.2, 1.0). 🌸
• GL_LIGHT_MODEL_COLOR_CONTROL — params must be either GL_SEPARATE_SPECULAR_COLOR or GL_SINGLE_COLOR. GL_SINGLE_COLOR specifies that a single color is generated from the lighting computation for a vertex. GL_SEPARATE_SPECULAR_COLOR specifies that the specular color computation of lighting be stored separately from the remainder of the lighting computation — and then the specular color is summed into the generated fragment's color after the application of texture mapping (if enabled). The initial value is GL_SINGLE_COLOR. ✨
• GL_LIGHT_MODEL_LOCAL_VIEWER — params is a single integer or floating-point value that specifies how specular reflection angles are computed. If params is 0 (or 0.0), specular reflection angles take the view direction to be parallel to and in the direction of the -z axis, regardless of the location of the vertex in eye coordinates. Otherwise, specular reflections are computed from the origin of the eye coordinate system. The initial value is 0. 🌈
• GL_LIGHT_MODEL_TWO_SIDE — params is a single integer or floating-point value that specifies whether one- or two-sided lighting calculations are done for polygons. It has no effect on the lighting calculations for points, lines, or bitmaps. If params is 0 (or 0.0), one-sided lighting is specified, and only the front material parameters are used in the lighting equation. Otherwise, two-sided lighting is specified. In this case, vertices of back-facing polygons are lighted using the back material parameters, and have their normals reversed before the lighting equation is evaluated. Vertices of front-facing polygons are always lighted using the front material parameters, with no change to their normals. The initial value is 0. 🫶

---

okay now the ✨math✨ section, and yes bestie it's a lot, but it's literally the lore of how your scene gets its color, so we're reading it together. 📖💖

In RGBA mode, the lighted color of a vertex is the sum of:

1. the material emission intensity,
2. the product of the material ambient reflectance and the lighting model full-scene ambient intensity,
3. and the contribution of each enabled light source.

Each light source contributes the sum of three terms: ambient, diffuse, and specular.

• The ambient light source contribution is the product of the material ambient reflectance and the light's ambient intensity.
• The diffuse light source contribution is the product of the material diffuse reflectance, the light's diffuse intensity, and the dot product of the vertex's normal with the normalized vector from the vertex to the light source.
• The specular light source contribution is the product of the material specular reflectance, the light's specular intensity, and the dot product of the normalized vertex-to-eye and vertex-to-light vectors, raised to the power of the shininess of the material.

All three light source contributions are attenuated equally based on the distance from the vertex to the light source and on light source direction, spread exponent, and spread cutoff angle. All dot products are replaced with 0 if they evaluate to a negative value. no negative dot products allowed in this house. 💀

The alpha component of the resulting lighted color is set to the alpha value of the material diffuse reflectance. periodt. 💅

In color index mode, the value of the lighted index of a vertex ranges from the ambient to the specular values passed to glMaterial using GL_COLOR_INDEXES. Diffuse and specular coefficients, computed with a (.30, .59, .11) weighting of the lights' colors, the shininess of the material, and the same reflection and attenuation equations as in the RGBA case, determine how much above ambient the resulting index is. 🌈

---

🎀 NOTES 🎀

GL_LIGHT_MODEL_COLOR_CONTROL is available only if the GL version is 1.2 or greater. bestie if you're on an older GL, that one's just not invited to the party. 😭

---

💀 ERRORS 💀

• GL_INVALID_ENUM is generated if pname is not an accepted value. 🙈
• GL_INVALID_ENUM is generated if pname is GL_LIGHT_MODEL_COLOR_CONTROL and params is not one of GL_SINGLE_COLOR or GL_SEPARATE_SPECULAR_COLOR.
• GL_INVALID_OPERATION is generated if glLightModel is executed between the execution of glBegin and the corresponding execution of glEnd. do NOT do this, the state machine will catch you. 🔥

---

🔍 ASSOCIATED GETS 🔍

• glGet with argument GL_LIGHT_MODEL_AMBIENT
• glGet with argument GL_LIGHT_MODEL_COLOR_CONTROL
• glGet with argument GL_LIGHT_MODEL_LOCAL_VIEWER
• glGet with argument GL_LIGHT_MODEL_TWO_SIDE
• glIsEnabled with argument GL_LIGHTING

---

🦋 SEE ALSO 🦋

glLight(3G), glMaterial(3G) — your two besties, go read them next, iykyk. 💖

---

and that's the whole page, bestie!! 🎉 this was the GLLIGHTMODEL page from the 3G manual, dated like every good 3G page is, and the footer literally just says GLLIGHTMODEL(3G) again because the man page format loves a lil bookend. slay, go light something up. 💅✨🌟