HYENA0 : Don't be boiled frog

// Updates the OpenGL view

- (void)drawView

{

// Make sure that you are drawing to the current context

[EAGLContext setCurrentContext:context];

glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);

glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

GLfloat matrix[4][4], length;

//Make sure we have a big enough acceleration vector

length = sqrtf(accel[0] * accel[0] + accel[1] * accel[1] + accel[2] * accel[2]);

//Setup model view matrix

glLoadIdentity();

glTranslatef(0.0, -0.1, -1.0);

glScalef(kTeapotScale, kTeapotScale, kTeapotScale);

if(length >= 0.1)

{

//Clear matrix to be used to rotate from the current referential to one based on the gravity vector

bzero(matrix, sizeof(matrix));

matrix[3][3] = 1.0;

//Setup first matrix column as gravity vector

matrix[0][0] = accel[0] / length;

matrix[0][1] = accel[1] / length;

matrix[0][2] = accel[2] / length;

//Setup second matrix column as an arbitrary vector in the plane perpendicular to the gravity vector {Gx, Gy, Gz} defined by by the equation "Gx * x + Gy * y + Gz * z = 0" in which we arbitrarily set x=0 and y=1

matrix[1][0] = 0.0;

matrix[1][1] = 1.0;

matrix[1][2] = -accel[1] / accel[2];

length = sqrtf(matrix[1][0] * matrix[1][0] + matrix[1][1] * matrix[1][1] + matrix[1][2] * matrix[1][2]);

matrix[1][0] /= length;

matrix[1][1] /= length;

matrix[1][2] /= length;

//Setup third matrix column as the cross product of the first two

matrix[2][0] = matrix[0][1] * matrix[1][2] - matrix[0][2] * matrix[1][1];

matrix[2][1] = matrix[1][0] * matrix[0][2] - matrix[1][2] * matrix[0][0];

matrix[2][2] = matrix[0][0] * matrix[1][1] - matrix[0][1] * matrix[1][0];

//Finally load matrix

glMultMatrixf((GLfloat*)matrix);

// Rotate a bit more so that its where we want it.

glRotatef(90.0, 0.0, 0.0, 1.0);

}

// If we're in the simulator we'd like to do something more interesting than just sit there

// But if we're on a device, we want to just let the accelerometer do the work for us without a fallback.

#if TARGET_IPHONE_SIMULATOR

else

{

static GLfloat spinX = 0.0, spinY = 0.0;

glRotatef(spinX, 0.0, 0.0, 1.0);

glRotatef(spinY, 0.0, 1.0, 0.0);

glRotatef(90.0, 1.0, 0.0, 0.0);

spinX += 1.0;

spinY += 0.25;

}

#endif

// Draw teapot. The new_teapot_indicies array is an RLE (run-length encoded) version of the teapot_indices array in teapot.h

for(int i = 0; i < num_teapot_indices; i += new_teapot_indicies[i] + 1)

{

glDrawElements(GL_TRIANGLE_STRIP, new_teapot_indicies[i], GL_UNSIGNED_SHORT, &new_teapot_indicies[i+1]);

}

glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);

[context presentRenderbuffer:GL_RENDERBUFFER_OES];

}

  주석에서 설명이 되어있으므로 주요한 설명은 안해도 될 것 같습니다.

  여기서 3차원 도형을 그리기 위한 주요한 내용만 다시 보겠습니다.

  단순히 도형만 그린다면 아래와 같이 고쳐볼 수 있습니다.

}

  위에서 glDrawElements 함수가 도형정보를 그리는 부분입니다. 

  주석에서처럼 teapot.h 파일에 num_teapot_indices, new_teapot_indices[i] 가 정의되어 있지요.

  이 부분이 어떻게 정의되는 지는 다음 포스트에서 봅시다.

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