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+
+//
+// TODO:
+// - what to do with ftransform? can it stay in the current form?
+// - implement texture1DLod, texture2DLod, texture3DLod, textureCubeLod,
+// - implement shadow1DLod, shadow2DLod,
+//
+
+//
+// From Shader Spec, ver. 1.10, rev. 59
+//
+// Some OpenGL operations still continue to occur in fixed functionality in between the vertex
+// processor and the fragment processor. Other OpenGL operations continue to occur in fixed
+// functionality after the fragment processor. Shaders communicate with the fixed functionality
+// of OpenGL through the use of built-in variables.
+//
+// The variable gl_Position is available only in the vertex language and is intended for writing
+// the homogeneous vertex position. All executions of a well-formed vertex shader must write
+// a value into this variable. It can be written at any time during shader execution. It may also
+// be read back by the shader after being written. This value will be used by primitive assembly,
+// clipping, culling, and other fixed functionality operations that operate on primitives after
+// vertex processing has occurred. Compilers may generate a diagnostic message if they detect
+// gl_Position is not written, or read before being written, but not all such cases are detectable.
+// Results are undefined if a vertex shader is executed and does not write gl_Position.
+//
+// The variable gl_PointSize is available only in the vertex language and is intended for a vertex
+// shader to write the size of the point to be rasterized. It is measured in pixels.
+//
+// The variable gl_ClipVertex is available only in the vertex language and provides a place for
+// vertex shaders to write the coordinate to be used with the user clipping planes. The user must
+// ensure the clip vertex and user clipping planes are defined in the same coordinate space. User
+// clip planes work properly only under linear transform. It is undefined what happens under
+// non-linear transform.
+//
+// These built-in vertex shader variables for communicating with fixed functionality are
+// intrinsically declared with the following types:
+//
+
+vec4 gl_Position; // must be written to
+float gl_PointSize; // may be written to
+vec4 gl_ClipVertex; // may be written to
+
+//
+// If gl_PointSize or gl_ClipVertex are not written to, their values are undefined. Any of these
+// variables can be read back by the shader after writing to them, to retrieve what was written.
+// Reading them before writing them results in undefined behavior. If they are written more than
+// once, it is the last value written that is consumed by the subsequent operations.
+//
+// These built-in variables have global scope.
+//
+
+//
+// The following attribute names are built into the OpenGL vertex language and can be used from
+// within a vertex shader to access the current values of attributes declared by OpenGL. All page
+// numbers and notations are references to the OpenGL 1.4 specification.
+//
+
+//
+// Vertex Attributes, p. 19.
+//
+
+attribute vec4 gl_Color;
+attribute vec4 gl_SecondaryColor;
+attribute vec3 gl_Normal;
+attribute vec4 gl_Vertex;
+attribute vec4 gl_MultiTexCoord0;
+attribute vec4 gl_MultiTexCoord1;
+attribute vec4 gl_MultiTexCoord2;
+attribute vec4 gl_MultiTexCoord3;
+attribute vec4 gl_MultiTexCoord4;
+attribute vec4 gl_MultiTexCoord5;
+attribute vec4 gl_MultiTexCoord6;
+attribute vec4 gl_MultiTexCoord7;
+attribute float gl_FogCoord;
+
+//
+// Unlike user-defined varying variables, the built-in varying variables don�t have a strict
+// one-to-one correspondence between the vertex language and the fragment language. Two sets are
+// provided, one for each language. Their relationship is described below.
+//
+// The following built-in varying variables are available to write to in a vertex shader.
+// A particular one should be written to if any functionality in a corresponding fragment shader
+// or fixed pipeline uses it or state derived from it. Otherwise, behavior is undefined.
+//
+
+varying vec4 gl_FrontColor;
+varying vec4 gl_BackColor;
+varying vec4 gl_FrontSecondaryColor;
+varying vec4 gl_BackSecondaryColor;
+varying vec4 gl_TexCoord[]; // at most will be gl_MaxTextureCoords
+varying float gl_FogFragCoord;
+
+//
+// For gl_FogFragCoord, the value written will be used as the �c� value on page 160 of the
+// OpenGL 1.4 Specification by the fixed functionality pipeline. For example, if the z-coordinate
+// of the fragment in eye space is desired as �c�, then that's what the vertex shader should write
+// into gl_FogFragCoord.
+//
+// As with all arrays, indices used to subscript gl_TexCoord must either be an integral constant
+// expressions, or this array must be re-declared by the shader with a size. The size can be
+// at most gl_MaxTextureCoords. Using indexes close to 0 may aid the implementation
+// in preserving varying resources.
+//
+
+//
+// The OpenGL Shading Language defines an assortment of built-in convenience functions for scalar
+// and vector operations. Many of these built-in functions can be used in more than one type
+// of shader, but some are intended to provide a direct mapping to hardware and so are available
+// only for a specific type of shader.
+//
+// The built-in functions basically fall into three categories:
+//
+// � They expose some necessary hardware functionality in a convenient way such as accessing
+// a texture map. There is no way in the language for these functions to be emulated by a shader.
+//
+// � They represent a trivial operation (clamp, mix, etc.) that is very simple for the user
+// to write, but they are very common and may have direct hardware support. It is a very hard
+// problem for the compiler to map expressions to complex assembler instructions.
+//
+// � They represent an operation graphics hardware is likely to accelerate at some point. The
+// trigonometry functions fall into this category.
+//
+// Many of the functions are similar to the same named ones in common C libraries, but they support
+// vector input as well as the more traditional scalar input.
+//
+// Applications should be encouraged to use the built-in functions rather than do the equivalent
+// computations in their own shader code since the built-in functions are assumed to be optimal
+// (e.g., perhaps supported directly in hardware).
+//
+// User code can replace built-in functions with their own if they choose, by simply re-declaring
+// and defining the same name and argument list.
+//
+
+//
+// Geometric Functions
+//
+// These operate on vectors as vectors, not component-wise.
+//
+
+//
+// For vertex shaders only. This function will ensure that the incoming vertex value will be
+// transformed in a way that produces exactly the same result as would be produced by OpenGL�s
+// fixed functionality transform. It is intended to be used to compute gl_Position, e.g.,
+// gl_Position = ftransform()
+// This function should be used, for example, when an application is rendering the same geometry in
+// separate passes, and one pass uses the fixed functionality path to render and another pass uses
+// programmable shaders.
+//
+
+vec4 ftransform () {
+ return gl_ModelViewProjectionMatrix * gl_Vertex;
+}
+
+//
+// 8.7 Texture Lookup Functions
+//
+// Texture lookup functions are available to both vertex and fragment shaders. However, level
+// of detail is not computed by fixed functionality for vertex shaders, so there are some
+// differences in operation between vertex and fragment texture lookups. The functions in the table
+// below provide access to textures through samplers, as set up through the OpenGL API. Texture
+// properties such as size, pixel format, number of dimensions, filtering method, number of mip-map
+// levels, depth comparison, and so on are also defined by OpenGL API calls. Such properties are
+// taken into account as the texture is accessed via the built-in functions defined below.
+//
+// If a non-shadow texture call is made to a sampler that represents a depth texture with depth
+// comparisons turned on, then results are undefined. If a shadow texture call is made to a sampler
+// that represents a depth texture with depth comparisions turned off, the results are undefined.
+// If a shadow texture call is made to a sampler that does not represent a depth texture, then
+// results are undefined.
+//
+// In all functions below, the bias parameter is optional for fragment shaders. The bias parameter
+// is not accepted in a vertex shader. For a fragment shader, if bias is present, it is added to
+// the calculated level of detail prior to performing the texture access operation. If the bias
+// parameter is not provided, then the implementation automatically selects level of detail:
+// For a texture that is not mip-mapped, the texture is used directly. If it is mip-mapped and
+// running in a fragment shader, the LOD computed by the implementation is used to do the texture
+// lookup. If it is mip-mapped and running on the vertex shader, then the base texture is used.
+//
+// The built-ins suffixed with �Lod� are allowed only in a vertex shader. For the �Lod� functions,
+// lod is directly used as the level of detail.
+//
+
+//
+// Use the texture coordinate coord to do a texture lookup in the 1D texture currently bound
+// to sampler. For the projective (�Proj�) versions, the texture coordinate coord.s is divided by
+// the last component of coord.
+//
+// XXX
+vec4 texture1DLod (sampler1D sampler, float coord, float lod) {
+ return vec4 (0.0);
+}
+vec4 texture1DProjLod (sampler1D sampler, vec2 coord, float lod) {
+ return texture1DLod (sampler, coord.s / coord.t, lod);
+}
+vec4 texture1DProjLod (sampler1D sampler, vec4 coord, float lod) {
+ return texture1DLod (sampler, coord.s / coord.q, lod);
+}
+
+//
+// Use the texture coordinate coord to do a texture lookup in the 2D texture currently bound
+// to sampler. For the projective (�Proj�) versions, the texture coordinate (coord.s, coord.t) is
+// divided by the last component of coord. The third component of coord is ignored for the vec4
+// coord variant.
+//
+// XXX
+vec4 texture2DLod (sampler2D sampler, vec2 coord, float lod) {
+ return vec4 (0.0);
+}
+vec4 texture2DProjLod (sampler2D sampler, vec3 coord, float lod) {
+ return texture2DLod (sampler, vec2 (coord.s / coord.p, coord.t / coord.p), lod);
+}
+vec4 texture2DProjLod (sampler2D sampler, vec4 coord, float lod) {
+ return texture2DLod (sampler, vec2 (coord.s / coord.q, coord.t / coord.q), lod);
+}
+
+//
+// Use the texture coordinate coord to do a texture lookup in the 3D texture currently bound
+// to sampler. For the projective (�Proj�) versions, the texture coordinate is divided by coord.q.
+//
+// XXX
+vec4 texture3DLod (sampler3D sampler, vec3 coord, float lod) {
+ return vec4 (0.0);
+}
+vec4 texture3DProjLod (sampler3D sampler, vec4 coord, float lod) {
+ return texture3DLod (sampler, vec3 (coord.s / coord.q, coord.t / coord.q, coord.s / coord.q),
+ lod);
+}
+
+//
+// Use the texture coordinate coord to do a texture lookup in the cube map texture currently bound
+// to sampler. The direction of coord is used to select which face to do a 2-dimensional texture
+// lookup in, as described in section 3.8.6 in version 1.4 of the OpenGL specification.
+//
+// XXX
+vec4 textureCubeLod (samplerCube sampler, vec3 coord, float lod) {
+ return vec4 (0.0);
+}
+
+//
+// Use texture coordinate coord to do a depth comparison lookup on the depth texture bound
+// to sampler, as described in section 3.8.14 of version 1.4 of the OpenGL specification. The 3rd
+// component of coord (coord.p) is used as the R value. The texture bound to sampler must be a
+// depth texture, or results are undefined. For the projective (�Proj�) version of each built-in,
+// the texture coordinate is divide by coord.q, giving a depth value R of coord.p/coord.q. The
+// second component of coord is ignored for the �1D� variants.
+//
+// XXX
+vec4 shadow1DLod (sampler1DShadow sampler, vec3 coord, float lod) {
+ return vec4 (0.0);
+}
+// XXX
+vec4 shadow2DLod (sampler2DShadow sampler, vec3 coord, float lod) {
+ return vec4 (0.0);
+}
+vec4 shadow1DProjLod(sampler1DShadow sampler, vec4 coord, float lod) {
+ return shadow1DLod (sampler, vec3 (coord.s / coord.q, 0.0, coord.p / coord.q), lod);
+}
+vec4 shadow2DProjLod(sampler2DShadow sampler, vec4 coord, float lod) {
+ return shadow2DLod (sampler, vec3 (coord.s / coord.q, coord.t / coord.q, coord.p / coord.q),
+ lod);
+}
+