绘制开放的gl纹理的一部分 [英] drawing part of open gl texture

问题描述

我试图仅画出我的子画面表的一部分.但是它只是缩放图像，而不会绘制图像宽度的1/3.我如何裁剪图像，所以只能显示1/3.文字在(ios 7，opengl es 2)-(GLKMatrix4)modelMatrix {

I am trying to draw only part of my sprite sheet. But it just scales the image and no drawing 1/3 of the width of the image. How can I crop the image so only 1/3 shows. Text is below ( ios 7,opengl es 2)- (GLKMatrix4) modelMatrix {

GLKMatrix4 modelMatrix = GLKMatrix4Identity;
modelMatrix = GLKMatrix4Translate(modelMatrix, x, y, 0);
return modelMatrix;

}
- (void)setSprite:(NSString *)fileName effect:(GLKBaseEffect *)newEffect {

// 1
self.effect = newEffect;

// 2
NSDictionary * options = [NSDictionary dictionaryWithObjectsAndKeys:
                              [NSNumber numberWithBool:YES],
                              GLKTextureLoaderOriginBottomLeft,
                              nil];

// 3
NSError * error;
NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:nil];

// 4
self.textureInfo = [GLKTextureLoader textureWithContentsOfFile:path options:options error:&error];
if (self.textureInfo == nil) {
    NSLog(@"Error loading file: %@", [error localizedDescription]);
        return ;
}

TexturedQuad newQuad;
newQuad.bl.geometryVertex = CGPointMake(0, 0);
newQuad.br.geometryVertex = CGPointMake(self.textureInfo.width, 0);
newQuad.tl.geometryVertex = CGPointMake(0, self.textureInfo.height);
newQuad.tr.geometryVertex = CGPointMake(self.textureInfo.width, self.textureInfo.height);

newQuad.bl.textureVertex = CGPointMake(0, 1);
newQuad.br.textureVertex = CGPointMake(1, 1);
newQuad.tl.textureVertex = CGPointMake(0, 0);
newQuad.tr.textureVertex = CGPointMake(1, 0);

self.quad = newQuad;

}

- (void)render {

// 1
self.effect.texture2d0.name = self.textureInfo.name;
self.effect.texture2d0.enabled = YES;

// 2
y++;
self.effect.transform.modelviewMatrix = self.modelMatrix;
[self.effect prepareToDraw];

// 3
glEnableVertexAttribArray(GLKVertexAttribPosition);
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);


// 4
TexturedQuad q;
q.bl.textureVertex = CGPointMake(0, 1);
q.br.textureVertex = CGPointMake(1, 1);
q.tl.textureVertex = CGPointMake(0, 0);
q.tr.textureVertex = CGPointMake(1, 0);
q.bl.geometryVertex = CGPointMake(0, 0);
q.br.geometryVertex = CGPointMake(self.textureInfo.width/3, 0);
q.tl.geometryVertex = CGPointMake(0, self.textureInfo.height);
q.tr.geometryVertex = CGPointMake(self.textureInfo.width/3, self.textureInfo.height);
long offset2 =(long)&q;
//long offset = (long)&_quad;
glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset2 + offsetof(TexturedVertex, geometryVertex)));
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset2 + offsetof(TexturedVertex, textureVertex)));

// 5
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

}

更新: TexturedQuad newQuad; newQuad.bl.geometryVertex = CGPointMake(0，0); newQuad.br.geometryVertex = CGPointMake(self.textureInfo.width/3，0); newQuad.tl.geometryVertex = CGPointMake(0，self.textureInfo.height); newQuad.tr.geometryVertex = CGPointMake(self.textureInfo.width/3，self.textureInfo.height);

Update: TexturedQuad newQuad; newQuad.bl.geometryVertex = CGPointMake(0, 0); newQuad.br.geometryVertex = CGPointMake(self.textureInfo.width/3, 0); newQuad.tl.geometryVertex = CGPointMake(0, self.textureInfo.height); newQuad.tr.geometryVertex = CGPointMake(self.textureInfo.width/3, self.textureInfo.height);

newQuad.bl.textureVertex = CGPointMake(0, 1);
newQuad.br.textureVertex = CGPointMake(.3, 1);
newQuad.tl.textureVertex = CGPointMake(0, 0);
newQuad.tr.textureVertex = CGPointMake(.3, 0);

推荐答案

这是纹理坐标的作用.您的"textureVertex"指定了映射到四边形的纹理的完整尺寸(0.0到1.0).您需要将其中一些值更改为1/3或2/3.例如:

That is what texture coordinates are for. Your 'textureVertex' is specifying the full dimensions of your texture (with 0.0 to 1.0) mapped to the quad. You need to change some of those values to either 1/3 or 2/3. For example:

newQuad.bl.textureVertex = CGPointMake(0, 0.33);
newQuad.br.textureVertex = CGPointMake(1, 1);
newQuad.tl.textureVertex = CGPointMake(0, 0.33);
newQuad.tr.textureVertex = CGPointMake(1, 0);

这篇关于绘制开放的gl纹理的一部分的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！