I need to draw graph.
I have to arrays of vertex attributes:
array of x coordinates: xPos
array of y coordinates: yPos
But X doesn't match Y.
I need to create separate arrays of indices and link them to the corresponding arrays of coordinates.
What i need
glEnableVertexAttribArray(opglp->xPositionLocation);
glBindBuffer(GL_ARRAY_BUFFER, opglp->vbo1);
glVertexAttribPointer(opglp->xPositionLocation, 1, GL_FLOAT, GL_FALSE, 0 , 0 );
glEnableVertexAttribArray(opglp->yPositionLocation);
glBindBuffer(GL_ARRAY_BUFFER, opglp->vbo2);
glVertexAttribPointer(opglp->yPositionLocation, 1, GL_FLOAT, GL_FALSE, 0 , 0 );
glDrawElements(GL_LINE_STRIP, 5, GL_UNSIGNED_SHORT, NULL);
Vertex shader:
attribute float xPosition;
attribute float yPosition;
uniform mat4 projection;
uniform mat4 modelView;
void main()
{
vec4 pos;
pos = vec4(xPosition, yPosition, 0.0, 1.0);
gl_Position = projection * modelView * pos;
}
Related
This problem is cocos2d-x related since I am using cocos2d-x as game engine but I can think it can be solved use basic opengl shader knowledge.
Part 1:
. I have a canvas size of 800 * 600
. I try to draw a simple colored square in size of 96 * 96 which is placed in the middle of the canvas
It is quite simple, the draw part code :
var boundingBox = this.getBoundingBox();
var squareVertexPositionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
var vertices = [
boundingBox.width, boundingBox.height,
0, boundingBox.height,
boundingBox.width, 0,
0, 0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
gl.bindBuffer(gl.ARRAY_BUFFER, null);
gl.enableVertexAttribArray(cc.VERTEX_ATTRIB_POSITION);
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
gl.vertexAttribPointer(cc.VERTEX_ATTRIB_POSITION, 2, gl.FLOAT, false, 0, 0);
gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
gl.bindBuffer(gl.ARRAY_BUFFER, null);
And the vert shader:
attribute vec4 a_position;
void main()
{
gl_Position = CC_PMatrix * CC_MVMatrix * a_position;
}
And the frag shader:
#ifdef GL_ES
precision highp float;
#endif
uniform vec2 center;
uniform vec2 resolution;
uniform float rotation;
void main()
{
vec4 RED = vec4(1.0, 0.0, 0.0, 1.0);
vec4 GREEN = vec4(0.0, 1.0, 0.0, 1.0);
gl_FragColor = GREEN;
}
And everything works fine :
The grid line is size of 32 * 32, and the black dot indicates the center of the canvas.
Part 2:
. I try to separate the square into half (vertically)
. The left part is green and the right part is red
I changed the frag shader to get it done :
void main()
{
vec4 RED = vec4(1.0, 0.0, 0.0, 1.0);
vec4 GREEN = vec4(0.0, 1.0, 0.0, 1.0);
/*
x => [0, 1]
y => [0, 1]
*/
vec2 UV = (rotatedFragCoord.xy - center.xy + resolution.xy / 2.0) / resolution.xy;
/*
x => [-1, 1]
y => [-1, 1]
*/
vec2 POS = -1.0 + 2.0 * UV;
if (POS.x <= 0.0) {
gl_FragColor = GREEN;
}
else {
gl_FragColor = RED;
}
}
The uniform 'center' is the position of the square so it is 400, 300 in this case.
The uniform 'resolution' is the content size of the square so the value is 96, 96.
The result is fine :
Part 3:
. I try to change the rotation in cocos2dx style
myShaderNode.setRotation(45);
And the square is rotated but the content is not :
So I tried to rotate the content according to the rotation angle of the node.
I changed the frag shader again:
void main()
{
vec4 RED = vec4(1.0, 0.0, 0.0, 1.0);
vec4 GREEN = vec4(0.0, 1.0, 0.0, 1.0);
vec2 rotatedFragCoord = gl_FragCoord.xy - center.xy;
float cosa = cos(rotation);
float sina = sin(rotation);
float t = rotatedFragCoord.x;
rotatedFragCoord.x = t * cosa - rotatedFragCoord.y * sina + center.x;
rotatedFragCoord.y = t * sina + rotatedFragCoord.y * cosa + center.y;
/*
x => [0, 1]
y => [0, 1]
*/
vec2 UV = (rotatedFragCoord.xy - center.xy + resolution.xy / 2.0) / resolution.xy;
/*
x => [-1, 1]
y => [-1, 1]
*/
vec2 POS = -1.0 + 2.0 * UV;
if (POS.x <= 0.0) {
gl_FragColor = GREEN;
}
else {
gl_FragColor = RED;
}
}
The uniform rotation is the angle the node rotated so in this case it is 45.
The result is close to what I want but still not right:
I tried hard but just can not figure out what is wrong in my code and what's more if there is anyway easier to get things done.
I am quite new to shader programming and any advice will be appreciated, thanks :)
Could I bind a vec2 array to a vec4 variable in shader language?
For example, in the code blow, the variable "position" is a vec4 type, and I tried to bind variable "squareVertices" to it, but squareVertices is a vec2 type array, only with (x,y) coodinates, maybe default (x,y,z,w) = (x,y,0,1)?
My Vertex shader and attribute bind code:
attribute vec4 position;
attribute vec2 textureCoordinate;
varying vec2 coordinate;
void main()
{
gl_Position = position;
coordinate = textureCoordinate;
}
glBindAttribLocation(gProgram, ATTRIB_VERTEX, "position");
glBindAttribLocation(gProgram, ATTRIB_TEXTURE, "textureCoordinate");
// bind attribute values
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_TEXTURE, 2, GL_FLOAT, 0, 0, coordVertices);
glEnableVertexAttribArray(ATTRIB_TEXTURE);
// squareVertices definition
static const GLfloat squareVertices[] = {
-1.0f, -1.0f,
0.0f, -1.0f,
-1.0f, 0.0f,
0.0f, 0.0f,
};
Yes, this is legal. And, you're correct that the default values of z and w are 0 and 1, respectively. This is covered in section 2.7 of the OpenGL ES 2.0 specification.
How to move object in world via glUniform**?
I tried glUniform3f(_positionSlot, 6.0f, 6.0f, -2.0f);
But my object not moving.
shader.vs:
attribute vec4 Position; // 1
attribute vec4 SourceColor; // 2
varying vec4 DestinationColor; // 3
uniform mat4 Projection;
uniform mat4 Modelview;
void main(void) { // 4
DestinationColor = SourceColor; // 5
gl_Position = Projection * Modelview *Position;
}
Reder:
- (void)render:(CADisplayLink*)displayLink {
glClearColor(0, 104.0/255.0, 55.0/255.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
CC3GLMatrix *projection = [CC3GLMatrix matrix];
float h = 4.0f * self.frame.size.height / self.frame.size.width;
[projection populateFromFrustumLeft:-2 andRight:2 andBottom:-h/2 andTop:h/2 andNear:4 andFar:10];
glUniformMatrix4fv(_projectionUniform, 1, 0, projection.glMatrix);
CC3GLMatrix *modelView = [CC3GLMatrix matrix];
[modelView populateFromTranslation:CC3VectorMake(sin(CACurrentMediaTime()), 0, -7)];
_currentRotation += displayLink.duration * 90;
[modelView rotateBy:CC3VectorMake(_currentRotation, _currentRotation, 0)];
glUniformMatrix4fv(_modelViewUniform, 1, 0, modelView.glMatrix);
// 1
glViewport(0, 0, self.frame.size.width, self.frame.size.height);
// 2
glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, 0, 0);
glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*) (sizeof(float) * 3));
glUniform4f(_colorSlot, 1.0f, 0.0f, 0.0f,1);
glDrawElements(GL_TRIANGLE_STRIP, 14, GL_UNSIGNED_SHORT, indices);
glUniform3f(_modelViewUniform, 6.0f, 6.0f, -2.0f);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer2);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
[_context presentRenderbuffer:GL_RENDERBUFFER];
}
EDIT:
_positionLocation=glGetAttribLocation(programHandle, "Translation");
glUniform3f(_positionLocation, -1.0f, 6.0f, -2.0f);
glDrawElements(GL_TRIANGLE_STRIP, 14, GL_UNSIGNED_SHORT, indices);
glUniform3f(_positionLocation, 1.0f, 6.0f, -2.0f);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer2);
If I draw only cube or only square all is ok. But seems that couple of it renders at same position and I see only cube. Seems that this method doesn't work.
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
gl_Position = Projection * Modelview * Position;
gl_Position is the vertex shader output that receives the transformed position of each vertex, not just the whole model. The "position slot" (varying/attribute) is used to pass vertex attribute data, namely each vertex position to the shader. You cannot apply a uniform to an attribute or varying. You need some additional uniform (let's call it "translation"):
attribute vec4 Position; // 1
attribute vec4 SourceColor; // 2
varying vec4 DestinationColor; // 3
uniform mat4 Projection;
uniform mat4 Modelview;
uniform vec4 Translation;
void main(void) { // 4
DestinationColor = SourceColor; // 5
gl_Position = Projection * Modelview * (Position + Translation);
}
Which you can set using with something like
glUniform3f(positionLocation, 6.0f, 6.0f, -2.0f);
BTW: Those are not called "slots", they're called "Locations".
My vertices are made up of an array with this structure:
[ Position ][ colour ]
[float][float][float][byte][byte][byte][byte]
Passing the vertex position is no problem:
gl.bindBuffer(gl.ARRAY_BUFFER, this.vbo);
gl.vertexAttribPointer(this.material.aVertexPosition, 3, gl.FLOAT, false, 4, 0);
But I can't figure out how I can pass the colours to the shader. Unfortunately, it's not possible to use integers inside the glsl shader so I have to use floats.
How can I get my unsigned byte colour value into the glsl float colour value? I tried it like this for r, g and b sepperately but the colours are all messed up:
gl.bindBuffer(gl.ARRAY_BUFFER, this.vbo);
gl.vertexAttribPointer(this.material.aR, 1, gl.BYTE, false, 15, 12);
Vertex Shader (colouredPoint.vs)
precision highp float;
attribute vec3 aVertexPosition;
attribute float aR;
attribute float aG;
attribute float aB;
uniform mat4 world;
uniform mat4 view;
uniform mat4 proj;
varying vec3 vVertexColour;
void main(void){
gl_PointSize = 4.0;
gl_Position = proj * view * world * vec4(aVertexPosition, 1.0);
vVertexColour = vec3(aR, aG, aB);
}
Pixel Shader (colouredPoint.fs)
precision highp float;
varying vec3 vVertexColour;
void main(void){
gl_FragColor = vec4(vVertexColour, 1);
}
gl.vertexAttribPointer(this.material.aVertexPosition, 3, gl.FLOAT, false, 4, 0);
gl.vertexAttribPointer(this.material.aR, 1, gl.BYTE, false, 15, 12);
Your stride should be 16, not 15 and certainly not 4.
Also, each individual color does not need to be a separate attribute. The four bytes can be a vec4 input. Oh, and your colors should be normalized, unsigned bytes. That is, the values on the range [0, 255] should be scaled to [0, 1] when the shader gets them. Therefore, what you want is:
gl.vertexAttribPointer(this.material.aVertexPosition, 3, gl.FLOAT, false, 16, 0);
gl.vertexAttribPointer(this.material.color, 4, gl.UNSIGNED_BYTE, true, 16, 12);
Oh, and attributes are not materials. You shouldn't call them that.
GLfloat red=(GLfloat)red/255;
I hope that's what you are looking for ^^
float pfIdentity[] =
{
-1.0f,0.0f,0.0f,0.0f,
0.0f,1.0f,0.0f,0.0f,
0.0f,0.0f,1.0f,0.0f,
0.0f,0.0f,0.0f,1.0f
};
==================================================================================
const char* pszVertShader = "\
attribute highp vec4 myVertex;\
uniform mediump mat4 myPMVMatrix;\
invariant gl_Position;\
void main(void)\
{\
gl_Position = myPMVMatrix * myVertex;\
}";
=====================================================================
for(int i = 0; i < 80000; ++i)
{
glClear(GL_COLOR_BUFFER_BIT);
int i32Location = glGetUniformLocation(uiProgramObject, "myPMVMatrix");
glUniformMatrix4fv( i32Location, 1, GL_FALSE, pfIdentity);
glEnableVertexAttribArray(VERTEX_ARRAY);
glVertexAttribPointer(VERTEX_ARRAY, 3, GL_FLOAT, GL_FALSE, 0, 0);
glDrawArrays(GL_TRIANGLES, 0,i);
eglSwapBuffers(eglDisplay, eglSurface);
}
return 0;
}
p.s : i am doing opengl-es in ubuntu 10.10 with kronos headers , its an emulator for opengl-es 2.0 in linux.
You don't have a projection at all. The Projection-Model-View matrix you're setting the myPMVMatrix uniform to is
float pfIdentity[] =
{
-1.0f,0.0f,0.0f,0.0f,
0.0f,1.0f,0.0f,0.0f,
0.0f,0.0f,1.0f,0.0f,
0.0f,0.0f,0.0f,1.0f
};
/* ... */
glUniformMatrix4fv( i32Location, 1, GL_FALSE, pfIdentity);
BTW: The idea of uniforms is, that you don't set them at each primitive iteration.
Anyway, this is a identity matrix, and since it's the only transformation applied it will just pass through the vertices as they are to the fragment stage. The solution for your problem is applying a orthographic projection to it, i.e. multiply that matrix with a ortho projection matrix and use the result of that operation instead. http://www.songho.ca/opengl/gl_projectionmatrix.html