ios - OpenGL ES 旋转二维纹理

Question

我是 OpenGL 的新手。我正在 iPad 上构建一个绘画应用程序，我有点关注 Apple 的 GLPaint例子。基本上我想在每次触摸移动时将纹理绘制到触摸位置。我能够从图像加载纹理并使用以下代码绘制它以查看:

初始化 GL:

- (BOOL)initGL {

glGenFramebuffers(1, &viewFramebuffer);
glGenRenderbuffers(1, &viewRenderbuffer);
glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(id<EAGLDrawable>)self.layer];
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, viewRenderbuffer);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);

if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
{
    NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
    return NO;
}

glViewport(0, 0, backingWidth, backingHeight);

glGenBuffers(1, &vboId);

brushTexture = [self textureFromName:@"Brush2.png"];

[self setupShaders];

glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

return YES;
}

加载纹理:

- (textureInfo_t)textureFromName:(NSString *)name {
CGImageRef      brushImage;
CGContextRef    brushContext;
GLubyte         *brushData;
size_t          width, height;
GLuint          texId;
textureInfo_t   texture;

brushImage = [UIImage imageNamed:name].CGImage;

width = CGImageGetWidth(brushImage);
height = CGImageGetHeight(brushImage);

if(brushImage) {
    brushData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
    brushContext = CGBitmapContextCreate(brushData, width, height, 8, width * 4, CGImageGetColorSpace(brushImage), kCGImageAlphaPremultipliedLast);
    CGContextDrawImage(brushContext, CGRectMake(0.0, 0.0, (CGFloat)width, (CGFloat)height), brushImage);

    CGContextRelease(brushContext);
    glGenTextures(1, &texId);
    glBindTexture(GL_TEXTURE_2D, texId);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (int)width, (int)height, 0, GL_RGBA, GL_UNSIGNED_BYTE, brushData);

    free(brushData);

    texture.id = texId;
    texture.width = (int)width;
    texture.height = (int)height;
}

return texture;
}

着色器:

- (void)setupShaders {
for (int i = 0; i < NUM_PROGRAMS; i++)
{
    char *vsrc = readFile(pathForResource(program[i].vert));
    char *fsrc = readFile(pathForResource(program[i].frag));
    GLsizei attribCt = 0;
    GLchar *attribUsed[NUM_ATTRIBS];
    GLint attrib[NUM_ATTRIBS];
    GLchar *attribName[NUM_ATTRIBS] = {
        "inVertex",
    };
    const GLchar *uniformName[NUM_UNIFORMS] = {
        "MVP", "pointSize", "vertexColor", "texture",
    };

    for (int j = 0; j < NUM_ATTRIBS; j++)
    {
        if (strstr(vsrc, attribName[j]))
        {
            attrib[attribCt] = j;
            attribUsed[attribCt++] = attribName[j];
        }
    }

    glueCreateProgram(vsrc, fsrc,
                      attribCt, (const GLchar **)&attribUsed[0], attrib,
                      NUM_UNIFORMS, &uniformName[0], program[i].uniform,
                      &program[i].id);
    free(vsrc);
    free(fsrc);

    if (i == PROGRAM_POINT)
    {
        glUseProgram(program[PROGRAM_POINT].id);

        glUniform1i(program[PROGRAM_POINT].uniform[UNIFORM_TEXTURE], 0);

        GLKMatrix4 projectionMatrix = GLKMatrix4MakeOrtho(0, backingWidth, 0, backingHeight, -1, 1);
        GLKMatrix4 modelViewMatrix = GLKMatrix4Identity; // this sample uses a constant identity modelView matrix
        GLKMatrix4 MVPMatrix = GLKMatrix4Multiply(projectionMatrix, modelViewMatrix);

        glUniformMatrix4fv(program[PROGRAM_POINT].uniform[UNIFORM_MVP], 1, GL_FALSE, MVPMatrix.m);

        glUniform1f(program[PROGRAM_POINT].uniform[UNIFORM_POINT_SIZE], brushTexture.width / kBrushScale);

        glUniform4fv(program[PROGRAM_POINT].uniform[UNIFORM_VERTEX_COLOR], 1, brushColor);
    }
}

glError();

绘制:

- (void)renderLineFromPoint:(CGPoint)start toPoint:(CGPoint)end {
static GLfloat*     vertexBuffer = NULL;
static NSUInteger   vertexMax = 64;
NSUInteger          vertexCount = 0,
                    count,
                    i;

[EAGLContext setCurrentContext:context];

glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);

CGFloat scale = self.contentScaleFactor;
start.x *= scale;
start.y *= scale;
end.x *= scale;
end.y *= scale;

if(vertexBuffer == NULL)
    vertexBuffer = malloc(vertexMax * 2 * sizeof(GLfloat));

count = MAX(ceilf(sqrtf((end.x - start.x) * (end.x - start.x) + (end.y - start.y) * (end.y - start.y)) / kBrushPixelStep), 1);
for(i = 0; i < count; ++i) {
    if(vertexCount == vertexMax) {
        vertexMax = 2 * vertexMax;
        vertexBuffer = realloc(vertexBuffer, vertexMax * 2 * sizeof(GLfloat));
    }

    vertexBuffer[2 * vertexCount + 0] = start.x + (end.x - start.x) * ((GLfloat)i / (GLfloat)count);
    vertexBuffer[2 * vertexCount + 1] = start.y + (end.y - start.y) * ((GLfloat)i / (GLfloat)count);
    vertexCount += 1;
}

glBindBuffer(GL_ARRAY_BUFFER, vboId);
glBufferData(GL_ARRAY_BUFFER, vertexCount*2*sizeof(GLfloat), vertexBuffer, GL_DYNAMIC_DRAW);

glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, GL_FALSE, 0, 0);

glUseProgram(program[PROGRAM_POINT].id);
glDrawArrays(GL_POINTS, 0, (int)vertexCount);

glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER];

我缺少的是一种在每次绘制之前旋转纹理的方法。我尝试使用旋转的 CGContext 初始化纹理，但是每次绘制一个点时都需要进行太多处理才能调用。有人可以告诉我一种更好的旋转纹理的方法吗？我是 OpenGL 的新手，我们将不胜感激。

Answer 1

您可以使用 GL_TEXTURE 矩阵模式将变换应用于纹理坐标。例如，将纹理坐标绕z轴逆时针旋转90度:

glMatrixMode(GL_TEXTURE);
glTranslatef(1.0f, 0.0f, 0.0f);
glRotatef(90.0f, 0.0f, 0.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);

注意在绕原点旋转后将纹理坐标范围保持在 [0.0, 1.0] 范围内的平移。我之前对类似问题的回答在这里更详细地解释了其中的一些内容:gluCylinder with rotated texture .

我通常会尽量避免推荐与张贴者询问的技术不同的技术，但在这种情况下我无能为力:如果您是 OpenGL ES 的新手，我强烈建议您跳过 ES 1.x。我相信现在大多数人会认为它是一个过时的 API。例如，如果您导航到 www.khronos.com (https://www.khronos.org/opengles/sdk/docs/) 上的手册页，您会注意到不再有指向 ES 1.x 的链接。如果您浏览更多内容，内容当然仍然存在，但它清楚地暗示 ES 2.0 如今被视为基线。