OpenGL Lighting on texture plane is not working

Question

I want to light to the texture plane but this is not work. Light on solid sphere is very well, but texture plane is not light.

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Answer 1

I want to light to the texture plane but this is not work. Light on solid sphere is very well, but texture plane is not light.

This is an issue caused by the Gouraud Shading model of the OpenGLs standard light model. While Phong shading in common means the technique, which does the light calculations per fragment, at Gouraud Shading, the light calculations are done per vertex. The calculated light is interpolated according to the Barycentric coordinate of the fragment on the primitive.

This means that in your case the light is calculated for the corners of the ground quad. This so calculated light is interpolated for all the fragments in between. The angel of the normal vector at the corners to the light vector tends to 90°. Because of that the entire ground quad looks almost unlit.

Since the light is calculated per vertex, then the light is calculated for more positions than the the 4 corners of the quad and the quality increases. Note, the light on the spheres looks almost perfect, because a sphere consists of a lot of vertices around its shape.

Try the following code, which splits the quad into tiles:

int   tiles = 5;
float u_max = height*tile_x;
float v_max = width*tile_x

glBegin(GL_QUADS);
glNormal3f(0, 1, 0);

for (int x=0; x < tiles; ++x)
{
    for (int y=0; y < tiles; ++y)
    {
        x0 = (float)x/(float)tiles;
        x1 = (float)(x+1)/(float)tiles;
        y0 = (float)y/(float)tiles;
        y1 = (float)(y+1)/(float)tiles;

        glTexCoord2f(u_max*x0, v_max*y0);  glVertex3f(height*x0, 0, widht*y0);
        glTexCoord2f(u_max*x1, v_max*y0);  glVertex3f(height*x0, 0, widht*y1);
        glTexCoord2f(u_max*x1, v_max*y1);  glVertex3f(height*x1, 0, widht*y1);
        glTexCoord2f(u_max*x0, v_max*y1);  glVertex3f(height*x1, 0, widht*y0);
    }
}
glEnd();

Of course you can also write your own shader and implement per fragment lighting. But the deprecated fixed function pipeline OpenGL standard light model does not support per fragment lighting.

See the difference in the WebGL example:

(function loadscene() {

var resize, gl, gouraudDraw, phongDraw, vp_size;
var bufSphere = {};

function render(delteMS){

    var shading = document.getElementById( "shading" ).value;
    var shininess = document.getElementById( "shininess" ).value;
    var ambientCol = [0.2, 0.2, 0.2];
    var diffuseCol = [0.6, 0.6, 0.6];
    var specularCol = [0.8, 0.8, 0.8];

    Camera.create();
    Camera.vp = vp_size;
        
    gl.enable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );

    gl.disable(gl.CULL_FACE);
    
    
    var progDraw = shading == 0 ? gouraudDraw : phongDraw;;
    // set up draw shader
    ShaderProgram.Use( progDraw.prog );
    ShaderProgram.SetUniformM44( progDraw.prog, "u_projectionMat44", Camera.Perspective() );
    ShaderProgram.SetUniformM44( progDraw.prog, "u_viewMat44", Camera.LookAt() );
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.lightPos", [0.0, 0.0, 0.25] )
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.ambient", ambientCol )
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.diffuse", diffuseCol )
    ShaderProgram.SetUniformF3( progDraw.prog, "u_lightSource.specular", specularCol )
    ShaderProgram.SetUniformF1( progDraw.prog, "u_lightSource.shininess", shininess )
    var modelMat = IdentityMat44()
    modelMat = RotateAxis( modelMat, -1.5, 0 );
    modelMat = RotateAxis( modelMat, CalcAng( delteMS, 17.0 ), 1 );
    ShaderProgram.SetUniformM44( progDraw.prog, "u_modelMat44", modelMat );
    
    // draw scene
    VertexBuffer.Draw( bufSphere );
   
    requestAnimationFrame(render);
}

function resize() {
    //vp_size = [gl.drawingBufferWidth, gl.drawingBufferHeight];
    vp_size = [window.innerWidth, window.innerHeight]
    canvas.width = vp_size[0];
    canvas.height = vp_size[1];
    gl.viewport( 0, 0, vp_size[0], vp_size[1] );
}

function initScene() {

    canvas = document.getElementById( "canvas");
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return null;

    gouraudDraw = {}
    gouraudDraw.prog = ShaderProgram.Create( 
      [ { source : "gouraud-shader-vs", stage : gl.VERTEX_SHADER },
        { source : "gouraud-shader-fs", stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_viewMat44", "u_modelMat44", 
        "u_lightSource.lightDir", "u_lightSource.ambient", "u_lightSource.diffuse", "u_lightSource.specular", "u_lightSource.shininess", ] );
    if ( gouraudDraw.prog == 0 )
      return;  
    gouraudDraw.inPos = gl.getAttribLocation( gouraudDraw.prog, "inPos" );
    gouraudDraw.inNV  = gl.getAttribLocation( gouraudDraw.prog, "inNV" );
    gouraudDraw.inCol = gl.getAttribLocation( gouraudDraw.prog, "inCol" );

    phongDraw = {}
    phongDraw.prog = ShaderProgram.Create( 
      [ { source : "phong-shader-vs", stage : gl.VERTEX_SHADER },
        { source : "phong-shader-fs", stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_viewMat44", "u_modelMat44", 
        "u_lightSource.lightDir", "u_lightSource.ambient", "u_lightSource.diffuse", "u_lightSource.specular", "u_lightSource.shininess", ] );
    if ( phongDraw.prog == 0 )
      return;
    phongDraw.inPos = gl.getAttribLocation( phongDraw.prog, "inPos" );
    phongDraw.inNV  = gl.getAttribLocation( phongDraw.prog, "inNV" );
    phongDraw.inCol = gl.getAttribLocation( phongDraw.prog, "inCol" );
    
    // create cube
    var layer_size = 16, circum_size = 32;
    var rad_circum = 1.0;
    var rad_tube = 0.5;
    var sphere_pts = [-1.0, -1.0, 0.0, 1.0, -1.0, 0.0, 1.0, 1.0, 0.0, -1.0, 1.0, 0.0];
    var sphere_nv  = [0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0];
    var sphere_col = [0.8, 0.6, 0.3, 0.8, 0.6, 0.3, 0.8, 0.6, 0.3, 0.8, 0.6, 0.3];
    var sphere_inx = [0, 1, 2, 0, 2, 3];
    bufSphere = VertexBuffer.Create(
    [ { data : sphere_pts, attrSize : 3, attrLoc : gouraudDraw.inPos },
      { data : sphere_nv, attrSize : 3, attrLoc : gouraudDraw.inNV },
      { data : sphere_col, attrSize : 3, attrLoc : gouraudDraw.inCol } ],
      sphere_inx );
      
    window.onresize = resize;
    resize();
    requestAnimationFrame(render);
}

function Fract( val ) { 
    return val - Math.trunc( val );
}
function CalcAng( deltaTime, intervall ) {
    return Fract( deltaTime / (1000*intervall) ) * 2.0 * Math.PI;
}
function CalcMove( deltaTime, intervall, range ) {
    var pos = self.Fract( deltaTime / (1000*intervall) ) * 2.0
    var pos = pos < 1.0 ? pos : (2.0-pos)
    return range[0] + (range[1] - range[0]) * pos;
}    
function EllipticalPosition( a, b, angRag ) {
    var a_b = a * a - b * b
    var ea = (a_b <= 0) ? 0 : Math.sqrt( a_b );
    var eb = (a_b >= 0) ? 0 : Math.sqrt( -a_b );
    return [ a * Math.sin( angRag ) - ea, b * Math.cos( angRag ) - eb, 0 ];
}

glArrayType = typeof Float32Array !="undefined" ? Float32Array : ( typeof WebGLFloatArray != "undefined" ? WebGLFloatArray : Array );

function IdentityMat44() {
  var m = new glArrayType(16);
  m[0]  = 1; m[1]  = 0; m[2]  = 0; m[3]  = 0;
  m[4]  = 0; m[5]  = 1; m[6]  = 0; m[7]  = 0;
  m[8]  = 0; m[9]  = 0; m[10] = 1; m[11] = 0;
  m[12] = 0; m[13] = 0; m[14] = 0; m[15] = 1;
  return m;
};

function RotateAxis(matA, angRad, axis) {
    var aMap = [ [1, 2], [2, 0], [0, 1] ];
    var a0 = aMap[axis][0], a1 = aMap[axis][1]; 
    var sinAng = Math.sin(angRad), cosAng = Math.cos(angRad);
    var matB = new glArrayType(16);
    for ( var i = 0; i < 16; ++ i ) matB[i] = matA[i];
    for ( var i = 0; i < 3; ++ i ) {
        matB[a0*4+i] = matA[a0*4+i] * cosAng + matA[a1*4+i] * sinAng;
        matB[a1*4+i] = matA[a0*4+i] * -sinAng + matA[a1*4+i] * cosAng;
    }
    return matB;
}

function Cross( a, b ) { return [ a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0], 0.0 ]; }
function Dot( a, b ) { return a[0]*b[0] + a[1]*b[1] + a[2]*b[2]; }
function Normalize( v ) {
    var len = Math.sqrt( v[0] * v[0] + v[1] * v[1] + v[2] * v[2] );
    return [ v[0] / len, v[1] / len, v[2] / len ];
}

var Camera = {};
Camera.create = function() {
    this.pos    = [0, 2, 0.0];
    this.target = [0, 0, 0];
    this.up     = [0, 0, 1];
    this.fov_y  = 90;
    this.vp     = [800, 600];
    this.near   = 0.5;
    this.far    = 100.0;
}
Camera.Perspective = function() {
    var fn = this.far + this.near;
    var f_n = this.far - this.near;
    var r = this.vp[0] / this.vp[1];
    var t = 1 / Math.tan( Math.PI * this.fov_y / 360 );
    var m = IdentityMat44();
    m[0]  = t/r; m[1]  = 0; m[2]  =  0;                              m[3]  = 0;
    m[4]  = 0;   m[5]  = t; m[6]  =  0;                              m[7]  = 0;
    m[8]  = 0;   m[9]  = 0; m[10] = -fn / f_n;                       m[11] = -1;
    m[12] = 0;   m[13] = 0; m[14] = -2 * this.far * this.near / f_n; m[15] =  0;
    return m;
}
Camera.LookAt = function() {
    var mz = Normalize( [ this.pos[0]-this.target[0], this.pos[1]-this.target[1], this.pos[2]-this.target[2] ] );
    var mx = Normalize( Cross( this.up, mz ) );
    var my = Normalize( Cross( mz, mx ) );
    var tx = Dot( mx, this.pos );
    var ty = Dot( my, this.pos );
    var tz = Dot( [-mz[0], -mz[1], -mz[2]], this.pos ); 
    var m = IdentityMat44();
    m[0]  = mx[0]; m[1]  = my[0]; m[2]  = mz[0]; m[3]  = 0;
    m[4]  = mx[1]; m[5]  = my[1]; m[6]  = mz[1]; m[7]  = 0;
    m[8]  = mx[2]; m[9]  = my[2]; m[10] = mz[2]; m[11] = 0;
    m[12] = tx;    m[13] = ty;    m[14] = tz;    m[15] = 1; 
    return m;
} 

var ShaderProgram = {};
ShaderProgram.Create = function( shaderList ) {
    var shaderObjs = [];
    for ( var i_sh = 0; i_sh < shaderList.length; ++ i_sh ) {
        var shderObj = this.CompileShader( shaderList[i_sh].source, shaderList[i_sh].stage );
        if ( shderObj == 0 )
            return 0;
        shaderObjs.push( shderObj );
    }
    var progObj = this.LinkProgram( shaderObjs )
    if ( progObj != 0 ) {
        progObj.attribIndex = {};
        var noOfAttributes = gl.getProgramParameter( progObj, gl.ACTIVE_ATTRIBUTES );
        for ( var i_n = 0; i_n < noOfAttributes; ++ i_n ) {
            var name = gl.getActiveAttrib( progObj, i_n ).name;
            progObj.attribIndex[name] = gl.getAttribLocation( progObj, name );
        }
        progObj.unifomLocation = {};
        var noOfUniforms = gl.getProgramParameter( progObj, gl.ACTIVE_UNIFORMS );
        for ( var i_n = 0; i_n < noOfUniforms; ++ i_n ) {
            var name = gl.getActiveUniform( progObj, i_n ).name;
            progObj.unifomLocation[name] = gl.getUniformLocation( progObj, name );
        }
    }
    return progObj;
}
ShaderProgram.AttributeIndex = function( progObj, name ) { return progObj.attribIndex[name]; } 
ShaderProgram.UniformLocation = function( progObj, name ) { return progObj.unifomLocation[name]; } 
ShaderProgram.Use = function( progObj ) { gl.useProgram( progObj ); } 
ShaderProgram.SetUniformI1  = function( progObj, name, val ) { if(progObj.unifomLocation[name]) gl.uniform1i( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformF1  = function( progObj, name, val ) { if(progObj.unifomLocation[name]) gl.uniform1f( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformF2  = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform2fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformF3  = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform3fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformF4  = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform4fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformM33 = function( progObj, name, mat ) { if(progObj.unifomLocation[name]) gl.uniformMatrix3fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.SetUniformM44 = function( progObj, name, mat ) { if(progObj.unifomLocation[name]) gl.uniformMatrix4fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.CompileShader = function( source, shaderStage ) {
    var shaderScript = document.getElementById(source);
    if (shaderScript)
      source = shaderScript.text;
    var shaderObj = gl.createShader( shaderStage );
    gl.shaderSource( shaderObj, source );
    gl.compileShader( shaderObj );
    var status = gl.getShaderParameter( shaderObj, gl.COMPILE_STATUS );
    if ( !status ) alert(gl.getShaderInfoLog(shaderObj));
    return status ? shaderObj : null;
} 
ShaderProgram.LinkProgram = function( shaderObjs ) {
    var prog = gl.createProgram();
    for ( var i_sh = 0; i_sh < shaderObjs.length; ++ i_sh )
        gl.attachShader( prog, shaderObjs[i_sh] );
    gl.linkProgram( prog );
    status = gl.getProgramParameter( prog, gl.LINK_STATUS );
    if ( !status ) alert("Could not initialise shaders");
    gl.useProgram( null );
    return status ? prog : null;
}

var VertexBuffer = {};
VertexBuffer.Create = function( attributes, indices ) {
    var buffer = {};
    buffer.buf = [];
    buffer.attr = []
    for ( var i = 0; i < attributes.length; ++ i ) {
        buffer.buf.push( gl.createBuffer() );
        buffer.attr.push( { size : attributes[i].attrSize, loc : attributes[i].attrLoc } );
        gl.bindBuffer( gl.ARRAY_BUFFER, buffer.buf[i] );
        gl.bufferData( gl.ARRAY_BUFFER, new Float32Array( attributes[i].data ), gl.STATIC_DRAW );
    }
    buffer.inx = gl.createBuffer();
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, buffer.inx );
    gl.bufferData( gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( indices ), gl.STATIC_DRAW );
    buffer.inxLen = indices.length;
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
    return buffer;
}
VertexBuffer.Draw = function( bufObj ) {
  for ( var i = 0; i < bufObj.buf.length; ++ i ) {
        gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.buf[i] );
        gl.vertexAttribPointer( bufObj.attr[i].loc, bufObj.attr[i].size, gl.FLOAT, false, 0, 0 );
        gl.enableVertexAttribArray( bufObj.attr[i].loc );
    }
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.drawElements( gl.TRIANGLES, bufObj.inxLen, gl.UNSIGNED_SHORT, 0 );
    for ( var i = 0; i < bufObj.buf.length; ++ i )
       gl.disableVertexAttribArray( bufObj.attr[i].loc );
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
}

initScene();

})();

html,body {
    height: 100%;
    width: 100%;
    margin: 0;
    overflow: hidden;
}

#gui {
    position : absolute;
    top : 0;
    left : 0;
}

  
  






    
Shading:
 
    
>
        Gouraud
        Phong
    
    

    
Shininess: