使用适用于iOS的OpenGL ES绘制正方形 [英] Draw Square with OpenGL ES for iOS

问题描述

我正在尝试使用apple提供的GLPaint示例项目绘制一个矩形.我尝试修改顶点，但无法在屏幕上显示矩形.手指画完美.我在renderRect方法中缺少什么吗?

I am trying to draw a rectangle using the GLPaint example project provided by apple. I have tried modifying the vertices but cannot get a rectangle to appear on the screen. The finger painting works perfectly. Am I missing something in my renderRect method?

- (void)renderRect {

    [EAGLContext setCurrentContext:context];
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);

    // Replace the implementation of this method to do your own custom drawing.
    static const GLfloat squareVertices[] = {
        -0.5f, -0.33f,
        0.5f, -0.33f,
        -0.5f,  0.33f,
        0.5f,  0.33f,
    };

    static float transY = 0.0f;

    glTranslatef(0.0f, (GLfloat)(sinf(transY)/2.0f), 0.0f);


    // Render the vertex array
    glVertexPointer(2, GL_FLOAT, 0, squareVertices);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);


    // Display the buffer
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];
}

该项目的其余部分均已设置好，以便可以在屏幕上绘制，但这些设置的gl设置仅供参考.

The rest of the project is set up stock to allow drawing on the screen but just for reference these are the gl settings that are set.

// Set the view's scale factor
self.contentScaleFactor = 1.0;

// Setup OpenGL states
glMatrixMode(GL_PROJECTION);
CGRect frame = self.bounds;
CGFloat scale = self.contentScaleFactor;
// Setup the view port in Pixels
glOrthof(0, frame.size.width * scale, 0, frame.size.height * scale, -1, 1);
glViewport(0, 0, frame.size.width * scale, frame.size.height * scale);
glMatrixMode(GL_MODELVIEW);

glDisable(GL_DITHER);
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_VERTEX_ARRAY);

glEnable(GL_BLEND);
// Set a blending function appropriate for premultiplied alpha pixel data
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

glEnable(GL_POINT_SPRITE_OES);
glTexEnvf(GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, GL_TRUE);
glPointSize(width / brushScale);   

推荐答案

问题是:

(1)以下代码:

    glMatrixMode(GL_PROJECTION);
    CGRect frame = self.bounds;
    CGFloat scale = self.contentScaleFactor;
    // Setup the view port in Pixels
    glOrthof(0, frame.size.width * scale, 0, frame.size.height * scale, -1, 1);
    glViewport(0, 0, frame.size.width * scale, frame.size.height * scale);

确定屏幕坐标的范围从左下角的(0，0)到右上角的frame.size.换句话说，一个OpenGL单元就是一个iPhone点.因此，您的数组:

Establishes that the on-screen coordinates range from (0, 0) in the lower left to frame.size in the upper right. In other words, one OpenGL unit is one iPhone point. So your array of:

static const GLfloat squareVertices[] = {
    -0.5f, -0.33f,
    0.5f, -0.33f,
    -0.5f,  0.33f,
    0.5f,  0.33f,
};

小于1像素.

(2)您在设置中具有以下内容:

(2) you have the following in the setup:

    brushImage = [UIImage imageNamed:@"Particle.png"].CGImage;

    /* ...brushImage eventually becomes the current texture... */

    glEnable(GL_TEXTURE_2D);

随后，您将无法为四边形提供纹理坐标.可能您想禁用GL_TEXTURE_2D.

You subsequently fail to supply texture coordinates for your quad. Probably you want to disable GL_TEXTURE_2D.

以下内容:

static const GLfloat squareVertices[] = {
    0.0f, 0.0f,
    0.0,  10.0f,
    90.0,  0.0f,
    90.0f, 10.0f,
};



glDisable(GL_TEXTURE_2D);
glColor4f(1.0f, 1.0f, 1.0f, 1.0f);

// Render the vertex array
glVertexPointer(2, GL_FLOAT, 0, squareVertices);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

将在屏幕的左下方产生一个白色的四边形，宽90点，宽10点.

Will produce a white quad 90 points wide and 10 points tlal in the lower left of the screen.

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