以下是我所想要得到的效果：

但我实际得到的却是这么个玩意儿：

找了很久很久，起初还以为是弄乱了opengl的状态机，

但是其他元素的渲染却并没有出什么问题啊，很奇怪，很纠结，很揪心。。

-(void) drawPolygon:(b2Fixture*)fixture xf:(b2Transform)xf color:(b2Color)color {

b2PolygonShape *poly = (b2PolygonShape*)fixture->GetShape();

int32 vertexCount = poly->m_vertexCount;

b2Vec2 vertices[b2_maxPolygonVertices];

for (int32 i = 0; i < vertexCount; ++ i) {

vertices[i] =b2Mul(xf, poly->m_vertices[i]);

vertices[i] +=b2Vec2(0.5f,30.0f -0.5f);

vertices[i] *=_gCfg.multiplyFactor /4;

}

glColor4f(color.r, color.g, color.b,_littleMapContentOpacity);

glVertexPointer(2, GL_FLOAT, 0, vertices);

glDrawArrays(GL_TRIANGLE_FAN,0, vertexCount);

}

后来发现是因为_littleMapContentOpacity这个成员变量在init方法里面没有被赋初值，着实害死我不少脑细胞~

// BYRender.h

@interface BYRender :NSObject {

GCfg *_gCfg;

BOOL _isCutLineValid; // 切割不合格的话会产生一道红色的残影线~

int _durationTimes;

float _touchPathMaxWidth;

float _littleMapContentOpacity; // 小地图内容的透明度~

int _cutLineDurationTimes;

}

@propertyBOOL isCutLineValid;

@propertyfloat touchPathMaxWidth;

@propertyfloat littleMapContentOpacity;

@propertyint cutLineDurationTimes;

......

// BYRender.mm

#import"BYRender.h"

@implementation BYRender

@synthesize isCutLineValid =_isCutLineValid;

@synthesize touchPathMaxWidth =_touchPathMaxWidth;

@synthesize littleMapContentOpacity =_littleMapContentOpacity;

@synthesize cutLineDurationTimes =_cutLineDurationTimes;

+ (BYRender*) getInstance {

staticBYRender *instance;

@synchronized(self) {

if (!instance) {

instance = [[BYRenderalloc]init];

}

}

return instance;

}

- (id) init {

if ((self = [superinit])) {

_gCfg = [GCfg getInstance];

_isCutLineValid =YES;

_durationTimes =0;

_littleMapContentOpacity = [_gCfgffk:@"littleMapContentOpacity"];

}

returnself;

}

还有一个要注意的问题：

(有些小细节不注意影响到了程序逻辑的话，找起来是很费劲的，必须要未雨绸缪)

在判断 NSString 是否等于 @"" 之前，最好还是先判断一下其是否为 nil~

if(valueStr!=nil && ![valueStr isEqualToString:@""]) {}