我正在尝试做一些基本的opengl编程来开始基础知识。
我有一个绘图功能试图绘制一个圆的楔形。出现问题,因为它实际上只是画了一个圆圈。
我仍然只是想在这里掌握opengl的基础知识。这是我到目前为止所拥有的。
- (void)drawView
{
[EAGLContext setCurrentContext:context];
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glViewport(0, 0, 60, 60);
int i;
float angle_start=90;
float angle_stop=180;
int segments=360;
float const angle_step = (angle_stop - angle_start)/segments;
GLfloat *arc_vertices;
arc_vertices = malloc(2*sizeof(GLfloat) * (segments+2));
arc_vertices[0] = arc_vertices[1] = 0.0;
for(i=0; i<segments+1; i++) {
arc_vertices[2 + 2*i ] = cos(angle_start + i*angle_step);
arc_vertices[2 + 2*i + 1] = sin(angle_start + i*angle_step);
}
glVertexPointer(2, GL_FLOAT, 0, arc_vertices);
glEnableClientState(GL_VERTEX_ARRAY);
glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, segments+2);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
free(arc_vertices);
}
答案 0 :(得分:1)
sin()
和cos()
将radians作为输入:
float angle_start=90;
float angle_stop=180;
int segments=360;
float const angle_step = (angle_stop - angle_start)/segments;
GLfloat* verts = (GLfloat*)malloc(2*sizeof(GLfloat) * (segments+2));
unsigned int pos = 0;
verts[pos++] = 0;
verts[pos++] = 0;
float radius = 10;
for( unsigned int i = 0; i < segments; ++i )
{
float rads = (angle_start + i*angle_step) * (3.14159 / 180);
verts[pos++] = ( cos( rads ) * radius );
verts[pos++] = ( sin( rads ) * radius );
}
glVertexPointer(2, GL_FLOAT, 0, verts);
glEnableClientState(GL_VERTEX_ARRAY);
glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, segments+1);
glDisableClientState(GL_VERTEX_ARRAY);
答案 1 :(得分:0)
我看错了。您可以访问顶点[i]和顶点[i + 1],但我总是增加1。
尝试替换
GLfloat顶点[720];
带
GLfloat顶点[2 * 720];
并替换
顶点[I] = P1; 顶点[I + 1] = P2;
通过
顶点[2 * I] = P1; 顶点[2 * I + 1] = P2;
答案 2 :(得分:0)
这有效。
抗锯齿是可怕的,但它的工作原理。 [信用1
-(void)drawcircelofSlice2
{
amt+=20;
if(amt>360.0)
{
amt=0;
}
[EAGLContext setCurrentContext:context];
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glViewport(20, 20, 50,50);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(30.0f, 30.0f, -1.5f, 1.5f, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
float x=0;
float y=0;
//float radius=20;
float lowAngle=0;
float highAngle=(amt/360) *360;
// float highAngle=360;
float numcirclePts=360;
lowAngle=DEGREES_TO_RADIANS(lowAngle);
highAngle=DEGREES_TO_RADIANS(highAngle);
float res=numcirclePts;
float angle=lowAngle;
float anglerange=highAngle-lowAngle;
float angleAdder=anglerange/ res;
int k=0;
GLfloat verts[720];
for (int i = 0; i < numcirclePts; i++){
verts[k] = x + cos(angle) ;
verts[k+1] = y - sin(angle) ;
angle += angleAdder;
k+=2;
}
verts[0] = x;
verts[1] = y;
k = 2;
for (int i = 2; i < numcirclePts; i++){
verts[k] = verts[k];
verts[k+1] = verts[k+1];
k+=2;
}
glVertexPointer(2, GL_FLOAT, 0, verts);
glEnableClientState(GL_VERTEX_ARRAY);
glColor4f(0.0f, 0.0f, 1.0f, 0.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, numcirclePts);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
glDisableClientState(GL_VERTEX_ARRAY);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
}